ci: add Codecov integration for code coverage reporting

[miclle]

Summary

This PR adds Codecov integration to automatically track and report code coverage metrics.

Changes

1. Added .codecov.yml configuration

• Coverage precision: 2 decimal places
• Coverage range: 70-100%
• Project coverage: Auto target with 1% threshold
• Patch coverage: Auto target with 1% threshold
• PR comments: Enabled with layout showing reach, diff, flags, and tree
• Ignores: Test files, examples, and testdata

2. Updated GitHub Actions workflow

• Added codecov/codecov-action@v5 step after test execution
• Upload coverage.txt generated by make test
• Only upload from ubuntu-latest to avoid duplicate reports
• Uses CODECOV_TOKEN secret for authentication
• Set fail_ci_if_error: false to not block CI on upload issues

Benefits

• ✅ Automatic coverage tracking on every commit
• ✅ Coverage reports on pull requests
• ✅ Visual diff showing coverage changes
• ✅ Historical coverage trends
• ✅ Badge in README already present and will now work

Setup Required

The repository maintainer needs to:

1. Sign up for Codecov at https://codecov.io/ (if not already done)
2. Add the repository to Codecov
3. Add CODECOV_TOKEN secret to GitHub repository settings:
   • Go to repository Settings → Secrets and variables → Actions
   • Add new secret named CODECOV_TOKEN
   • Get the token from Codecov dashboard

Testing

Once the secret is added, the workflow will:

• Run tests and generate coverage report
• Upload to Codecov automatically
• Display coverage on Codecov dashboard
• Add coverage comments to PRs

References

• Codecov documentation: https://docs.codecov.com/docs
• GitHub Action: https://github.com/codecov/codecov-action

[codecov]

Welcome to Codecov 🎉

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 ☂️