Add support for code coverage

[michael-christen]

Utilize bazel coverage to get coverage information

Utilizes https://github.com/linux-test-project/lcov (installed with https://github.com/hrishikesh-kadam/setup-lcov)

• A decent reverse engineering perspective of lcov: https://github.com/ChrisTimperley/lcovparser.py/blob/main/lcovparser.py
• Here is how to exclude lines: https://stackoverflow.com/questions/23264049/how-to-tell-lcov-to-ignore-lines-in-the-source-files

Uploads to codecov

• See https://github.com/codecov/codecov-action for configuration of the github action

See https://groups.google.com/g/bazel-discuss/c/igMsIXf0kUQ and https://github.com/bazelbuild/bazel/issues/19357 for a discussion of why bazel doesn't get you "all source files" in coverage.

TODO

• [x] add all source files in a baseline.dat that I generate to not get an inflated coverage if something isn't covered at all

Followups

• Is there a better way to install lcov (part of the image)?
• Add a badge to README https://app.codecov.io/github/michael-christen/toolbox/config/badge
• Try out including embedded coverage: https://github.com/nasa-jpl/embedded-gcov/blob/main/example/example.c / https://www.thanassis.space/coverage.html perhaps https://developer.arm.com/documentation/ihi0014/q/Introduction/About-Embedded-Trace-Macrocells and https://www.trustedfirmware.org/docs/TracebasedCodeCoverageTooling.pdf
• If codecov becomes a pain, try out https://github.com/marketplace/actions/report-lcov
• Maybe I should simply setup a check to compare source files against what is transitively included in tests?

[codecov-commenter]

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.

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