Scaffold out code coverage reporting implementation

[Blacksmoke16]

Context

Resolves #450.

Changelog

• Update scripts/test.sh to optionally allow generating of code coverage
• Revert https://github.com/athena-framework/athena/pull/406
  • This just makes things easier for generating the reports, can follow up to improve again if needed. Either by seeing about building on macos-latest itself again, or using actions/cache to not build it every time
• Configure https://app.codecov.io/gh/athena-framework/athena

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Before merging, remember to add the athena-framework/athena prefix to the PR number in the PR title

[Blacksmoke16]

This is proving to be not as straightforward as I was initially thinking. There are no pre-built binaries for kcov so I can't just fetch them via curl or install via apt or something. There is a homebrew package, but when used on the macos-latest image it seems broken: https://github.com/athena-framework/athena/actions/runs/11094736512/job/30822531929?pr=451.

The compiled specs are also running on macos-latest for a reason: https://github.com/athena-framework/athena/pull/406, so changing it would essentially be reverting that PR.

Also as I discovered in https://github.com/crystal-lang/crystal/issues/1157#issuecomment-2381352644, the compiled tests would treat the unit tests as having 0% coverage which isn't ideal. So it might be easiest to just have coverage be its own CI job that does both unit and compiled in one batch. This way we only have to build kcov once and good to go? Not a fan of essentially running the specs twice, so I'll keep thinking on this for now...

[codecov[bot]]

Welcome to Codecov :tada:

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

:information_source: You can also turn on project coverage checks and project coverage reporting on Pull Request comment

Thanks for integrating Codecov - We've got you covered :open_umbrella: