ci: replace codecov with GitHub native coverage reporting

[riccardo-negri]

Replace the codecov.io-based coverage job in ci.yml with cargo llvm-cov --cobertura and actions/upload-code-coverage@v1 to report coverage natively on GitHub. Remove codecov.yml.

[Copilot]

Pull request overview

This PR migrates CI coverage reporting from Codecov to GitHub’s native code coverage upload API by switching the coverage artifact format to Cobertura XML and using actions/upload-code-coverage@v1.

Changes:

• Update the coverage job to generate a Cobertura report via cargo llvm-cov --cobertura and upload it with actions/upload-code-coverage@v1.
• Add job-level permissions required for native coverage upload (code-quality: write).
• Remove the repository’s Codecov configuration file (.github/codecov.yml).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.github/workflows/ci.yml	Switch coverage generation to Cobertura XML and upload coverage to GitHub natively with required permissions.
.github/codecov.yml	Remove Codecov-specific configuration as part of decommissioning Codecov reporting.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[riccardo-negri]

From https://github.com/actions/upload-code-coverage I read that

Fork PRs are not supported. Pull requests from forks don't have write access to the base repository, so the action cannot upload coverage. When a fork PR is detected, the action exits gracefully with a notice — it won't fail your CI.

Therefore GitHub native code coverage is not suitable for now.