[llbbl]

Summary

• Add PCOV-based PHP coverage collection and Clover reporting to pull-request CI.
• Upload coverage through Codecov OIDC with project and patch thresholds plus PR comments.
• Document the baseline, local commands, coverage badge, and testing workflow.

Changes

Build System

• .github/workflows/ci.yml: Enable PCOV, run the fast coverage suite on pull requests, and upload Clover output to Codecov using OIDC.
• codecov.yml: Configure project and patch coverage thresholds and pull-request comment output.
• composer.json: Produce Clover and HTML coverage reports from the fast PHP suite.
• phpunit.xml.dist: Include uncovered source files in coverage reporting.

Documentation

• README.md: Add the Codecov status badge.
• docs/testing.md: Document coverage commands, baseline, exclusions, and interpretation.
• docs/testing-procedures.md: Record baseline, long-term, and pull-request coverage targets.

Test plan

• composer validate --strict
• composer test (198 tests, 606 assertions)
• Coverage run with PCOV producing Clover/HTML at 40.54%
• composer test:integration (59 tests, 470 assertions)
• composer analyse
• composer cs-check
• pnpm check
• pnpm api:lint
• actionlint
• Official Codecov YAML validator
• Independent PHP review: PASS
• Independent CI/config review: PASS

Closes #135

[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 ☂️