feat: add codecov coverage reporting to CI workflow

[CrashBytes]

Adds coverage reporting to the React Compatibility workflow:

• Runs tests with coverage using npm run test:coverage
• Uploads coverage to Codecov (React 18 only to avoid duplicates)
• Uses lcov.info format for coverage reports
• No CODECOV_TOKEN needed for public repos

This enables:

• ✅ Coverage tracking on Codecov
• ✅ PR coverage diffs
• ✅ Coverage badges
• ✅ Historical coverage trends

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot

See analysis details on SonarQube Cloud

[codecov-commenter]

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.

ℹ️ 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 ☂️