Configure code coverage reporting

[xushiyan]

Update 2024-05-09

Got codecov token available and this is fixed in #20

Update 2024-05-06

Sonar cloud does not support

• rust lang for code coverage reporting despite community asks over a few years
• asf sonarcloud token is not usable on forked repo PRs, meaning it's not feasible to report coverage in PRs which come from fork almost all the time
• community maintained tool cargo-sonar does not support coverage reporting either. The supported tools like clippy, audit, etc should be enforced on PRs, instead of post-reporting from main branch. Hence cargo-sonar not a choice here.

2 possible solutions

• ask for asf assistance in adding codecov token in GH secret - adopting codecov solves the problem
• mitigation: without reporting service, comment plain text as PR comment for coverage reporting
  • GHA https://github.com/marketplace/actions/comment-pull-request
  • using output from tarpaulin or grcov

Update 2024-05-05

See description in #17 (comment)