ci: cleanup into a single per-pr.yml gha

[samlaf]

Much needed cleanup of CI pipelines. We now have 2 main pipelines:

• one that runs on every PR: runs tests, lint, builds
• one that runs on every release: pushes image to GHCR

Only downside of this cleanup is that we can't have separate README badges for the different jobs (GHA only allows one badge for the entire workflow). Personally I prefer having a cleaner CI than extra precision of badges on the repo.

Even considering switching our CI to use https://docs.dagger.io/ at some point.

Fixes Issue

Fixes #

Changes proposed

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Note to reviewers

We will have to update the required workflows in the github repo settings. The old workflows that have been deleted (but are still required) will never pass. We should prob update them right before merging this PR. I can do that once this PR is approved.

[litt3]

LGTM

[ethenotethan]

not a big fan of this change tbh. would prefer to have separate workflows given differing checks vs restructuring the file schema to be workflows specific to dispatch conditions. IMO restructuring or consolidating would make sense with workflows that have overlapping dependencies (e.g, linting and testing both use a golang job for initializing the language dependency in the runner's environment). Also have never seen this pattern before (e.g, in the eigenda repo we delineate workflows based on higher order checks). Anyways if this is smth we'd like to adopt I'd prefer at a minimum we change the workflow file name from per-pr.yml to something like action.yml

[ethenotethan]

LGTM

[ethenotethan]

LGTM