Improves CI, fixes no_std and other misc issues discovered

.github/DOCS.md

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+# Github config and workflows
+
+In this folder there is configuration for codecoverage, dependabot, and ci
+workflows that check the library more deeply than the default configurations.
+
+This folder can be or was merged using a --allow-unrelated-histories merge
+strategy from <https://github.com/jonhoo/rust-ci-conf/> which provides a
+reasonably sensible base for writing your own ci on. By using this strategy
+the history of the CI repo is included in your repo, and future updates to
+the CI can be merged later.
+
+To perform this merge run:
+
+```shell
+git remote add ci https://github.com/jonhoo/rust-ci-conf.git
+git fetch ci
+git merge --allow-unrelated-histories ci/main
+```
+
+An overview of the files in this project is available at:
+<https://www.youtube.com/watch?v=xUH-4y92jPg&t=491s>, which contains some
+rationale for decisions and runs through an example of solving minimal version
+and OpenSSL issues.

.github/codecov.yml

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+# ref: https://docs.codecov.com/docs/codecovyml-reference
+coverage:
+  # Hold ourselves to a high bar
+  range: 85..100
+  round: down
+  precision: 1
+  status:
+    # ref: https://docs.codecov.com/docs/commit-status
+    project:
+      default:
+        # Avoid false negatives
+        threshold: 1%
+
+# Test files aren't important for coverage
+ignore:
+  - "tests"
+
+# Make comments less noisy
+comment:
+  layout: "files"
+  require_changes: true

.github/dependabot.yml

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+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily
+  - package-ecosystem: cargo
+    directory: /
+    schedule:
+      interval: daily
+    ignore:
+      - dependency-name: "*"
+        # patch and minor updates don't matter for libraries as consumers of this library build
+        # with their own lockfile, rather than the version specified in this library's lockfile
+        # remove this ignore rule if your package has binaries to ensure that the binaries are
+        # built with the exact set of dependencies and those are up to date.
+        update-types:
+          - "version-update:semver-patch"
+          - "version-update:semver-minor"

.github/workflows/check.yml

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+# This workflow runs whenever a PR is opened or updated, or a commit is pushed to main. It runs
+# several checks:
+# - fmt: checks that the code is formatted according to rustfmt
+# - clippy: checks that the code does not contain any clippy warnings
+# - doc: checks that the code can be documented without errors
+# - hack: check combinations of feature flags
+# - msrv: check that the msrv specified in the crate is correct
+permissions:
+    contents: read
+# This configuration allows maintainers of this repo to create a branch and pull request based on
+# the new branch. Restricting the push trigger to the main branch ensures that the PR only gets
+# built once.
+on:
+    push:
+        branches: [main]
+    pull_request:
+# If new code is pushed to a PR branch, then cancel in progress workflows for that PR. Ensures that
+# we don't waste CI time, and returns results quicker https://github.com/jonhoo/rust-ci-conf/pull/5
+concurrency:
+    group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+    cancel-in-progress: true
+name: check
+jobs:
+    fmt:
+        runs-on: ubuntu-latest
+        name: stable / fmt
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install stable
+              uses: dtolnay/rust-toolchain@stable
+              with:
+                  components: rustfmt
+            - name: cargo fmt --check
+              run: cargo fmt --check
+    clippy:
+        runs-on: ubuntu-latest
+        name: ${{ matrix.toolchain }} / clippy
+        permissions:
+            contents: read
+            checks: write
+        strategy:
+            fail-fast: false
+            matrix:
+                # Get early warning of new lints which are regularly introduced in beta channels.
+                toolchain: [stable, beta]
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install ${{ matrix.toolchain }}
+              uses: dtolnay/rust-toolchain@master
+              with:
+                  toolchain: ${{ matrix.toolchain }}
+                  components: clippy
+            - name: cargo clippy
+              uses: giraffate/clippy-action@v1
+              with:
+                  reporter: "github-pr-check"
+                  github_token: ${{ secrets.GITHUB_TOKEN }}
+    semver:
+        runs-on: ubuntu-latest
+        name: semver
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install stable
+              uses: dtolnay/rust-toolchain@stable
+              with:
+                  components: rustfmt
+            - name: cargo-semver-checks
+              uses: obi1kenobi/cargo-semver-checks-action@v2
+    doc:
+        # run docs generation on nightly rather than stable. This enables features like
+        # https://doc.rust-lang.org/beta/unstable-book/language-features/doc-cfg.html which allows an
+        # API be documented as only available in some specific platforms.
+        runs-on: ubuntu-latest
+        name: nightly / doc
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install nightly
+              uses: dtolnay/rust-toolchain@nightly
+            - name: cargo doc
+              run: cargo doc --no-deps --all-features
+              env:
+                  RUSTDOCFLAGS: --cfg docsrs
+    hack:
+        # cargo-hack checks combinations of feature flags to ensure that features are all additive
+        # which is required for feature unification
+        runs-on: ubuntu-latest
+        name: ubuntu / stable / features
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install stable
+              uses: dtolnay/rust-toolchain@stable
+            - name: cargo install cargo-hack
+              uses: taiki-e/install-action@cargo-hack
+            # intentionally no target specifier; see https://github.com/jonhoo/rust-ci-conf/pull/4
+            # --feature-powerset runs for every combination of features
+            - name: cargo hack
+              run: cargo hack --feature-powerset check
+    msrv:
+        # check that we can build using the minimal rust version that is specified by this crate
+        runs-on: ubuntu-latest
+        # we use a matrix here just because env can't be used in job names
+        # https://docs.github.com/en/actions/learn-github-actions/contexts#context-availability
+        strategy:
+            matrix:
+                msrv: ["1.76"]
+        name: ubuntu / ${{ matrix.msrv }}
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install ${{ matrix.msrv }}
+              uses: dtolnay/rust-toolchain@master
+              with:
+                  toolchain: ${{ matrix.msrv }}
+            - name: cargo +${{ matrix.msrv }} check
+              run: cargo check

.github/workflows/nostd.yml

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+# This workflow checks whether the library is able to run without the std library (e.g., embedded).
+# This entire file should be removed if this crate does not support no-std. See check.yml for
+# information about how the concurrency cancellation and workflow triggering works
+permissions:
+  contents: read
+on:
+  push:
+    branches: [main]
+  pull_request:
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+name: no-std
+jobs:
+  nostd:
+    runs-on: ubuntu-latest
+    name: ${{ matrix.target }}
+    strategy:
+      matrix:
+        target: [thumbv7m-none-eabi, aarch64-unknown-none]
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+      - name: Install stable
+        uses: dtolnay/rust-toolchain@stable
+      - name: rustup target add ${{ matrix.target }}
+        run: rustup target add ${{ matrix.target }}
+      - name: cargo check
+        run: cargo check --target ${{ matrix.target }} --no-default-features

.github/workflows/safety.yml

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+# This workflow runs checks for unsafe code. In crates that don't have any unsafe code, this can be
+# removed. Runs:
+# - miri - detects undefined behavior and memory leaks
+# - address sanitizer - detects memory errors
+# - leak sanitizer - detects memory leaks
+# See check.yml for information about how the concurrency cancellation and workflow triggering works
+permissions:
+    contents: read
+on:
+    push:
+        branches: [main]
+    pull_request:
+concurrency:
+    group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+    cancel-in-progress: true
+name: safety
+jobs:
+    sanitizers:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - name: Install nightly
+              uses: dtolnay/rust-toolchain@nightly
+            - run: |
+                  # to get the symbolizer for debug symbol resolution
+                  sudo apt install llvm
+                  # to fix buggy leak analyzer:
+                  # https://github.com/japaric/rust-san#unrealiable-leaksanitizer
+                  # ensure there's a profile.dev section
+                  if ! grep -qE '^[ \t]*[profile.dev]' Cargo.toml; then
+                      echo >> Cargo.toml
+                      echo '[profile.dev]' >> Cargo.toml
+                  fi
+                  # remove pre-existing opt-levels in profile.dev
+                  sed -i '/^\s*\[profile.dev\]/,/^\s*\[/ {/^\s*opt-level/d}' Cargo.toml
+                  # now set opt-level to 1
+                  sed -i '/^\s*\[profile.dev\]/a opt-level = 1' Cargo.toml
+                  cat Cargo.toml
+              name: Enable debug symbols
+            - name: cargo test -Zsanitizer=address
+              # only --lib --tests b/c of https://github.com/rust-lang/rust/issues/53945
+              run: cargo test --lib --tests --all-features --target x86_64-unknown-linux-gnu
+              env:
+                  ASAN_OPTIONS: "detect_odr_violation=0:detect_leaks=0"
+                  RUSTFLAGS: "-Z sanitizer=address"
+            - name: cargo test -Zsanitizer=leak
+              if: always()
+              run: cargo test --all-features --target x86_64-unknown-linux-gnu
+              env:
+                  LSAN_OPTIONS: "suppressions=lsan-suppressions.txt"
+                  RUSTFLAGS: "-Z sanitizer=leak"
+    miri:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  submodules: true
+            - run: |
+                  echo "NIGHTLY=nightly-$(curl -s https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/miri)" >> $GITHUB_ENV
+            - name: Install ${{ env.NIGHTLY }}
+              uses: dtolnay/rust-toolchain@master
+              with:
+                  toolchain: ${{ env.NIGHTLY }}
+                  components: miri
+            - name: cargo miri test
+              run: cargo miri test -- --skip pointer::tests::qc
+              env:
+                  MIRIFLAGS: ""

.github/workflows/scheduled.yml

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+# Run scheduled (rolling) jobs on a nightly basis, as your crate may break independently of any
+# given PR. E.g., updates to rust nightly and updates to this crates dependencies. See check.yml for
+# information about how the concurrency cancellation and workflow triggering works
+permissions:
+  contents: read
+on:
+  push:
+    branches: [main]
+  pull_request:
+  schedule:
+    - cron:  '7 7 * * *'
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+name: rolling
+jobs:
+  # https://twitter.com/mycoliza/status/1571295690063753218
+  nightly:
+    runs-on: ubuntu-latest
+    name: ubuntu / nightly
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+      - name: Install nightly
+        uses: dtolnay/rust-toolchain@nightly
+      - name: cargo generate-lockfile
+        if: hashFiles('Cargo.lock') == ''
+        run: cargo generate-lockfile
+      - name: cargo test --locked
+        run: cargo test --locked --all-features --all-targets
+  # https://twitter.com/alcuadrado/status/1571291687837732873
+  update:
+    # This action checks that updating the dependencies of this crate to the latest available that
+    # satisfy the versions in Cargo.toml does not break this crate. This is important as consumers
+    # of this crate will generally use the latest available crates. This is subject to the standard
+    # Cargo semver rules (i.e cargo does not update to a new major version unless explicitly told
+    # to).
+    runs-on: ubuntu-latest
+    name: ubuntu / beta / updated
+    # There's no point running this if no Cargo.lock was checked in in the first place, since we'd
+    # just redo what happened in the regular test job. Unfortunately, hashFiles only works in if on
+    # steps, so we repeat it.
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+      - name: Install beta
+        if: hashFiles('Cargo.lock') != ''
+        uses: dtolnay/rust-toolchain@beta
+      - name: cargo update
+        if: hashFiles('Cargo.lock') != ''
+        run: cargo update
+      - name: cargo test
+        if: hashFiles('Cargo.lock') != ''
+        run: cargo test --locked --all-features --all-targets
+        env:
+          RUSTFLAGS: -D deprecated