chore: migrate to nextest and llvm-cov for unit tests and coverage

[nshirley]

Description

Describe these changes.

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This migrates unit test to use nextest and cargo-llvm-cov to support integration with the ete test pipeline

• In addition to moving to nextest, the workflows now use the makefile test commands for consistency running locally vs. in ci
• There are a few extra variables in the Makefile in preparation for integration tests reporting as well
• I removed the --workspace flag for now, too, since it was causing issues with a failed build. It can be added back in once the underlying crate is fixed

Testing

How should reviewers test?

• Unit tests should still pass in CI
• There should also be an output/captured test results in CI

Issue(s)

Closes SYNC-4611.