CI: adding cython coverage
- [x] closes #43652

Trying to include cython codes in codecov reports.
Working with the CI for the first time.

@debnathshoham - do you still want to work on this? See comments above - H2H if needed This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. closing as stale