Add coverage workflow entry to CHANGELOG.md

Co-authored-by: talgalili <976006+talgalili@users.noreply.github.com>

Author: Copilot

CHANGELOG.md

@@ -77,6 +77,7 @@
 
 ## Tests
 - **Added Pyre type checking to GitHub Actions** via `.pyre_configuration.external` and a new `pyre` job in the workflow. Tests are excluded due to external typeshed stub differences; library code is fully type-checked.
+- **Added test coverage workflow and badge to README** via `.github/workflows/coverage.yml`. The workflow collects coverage using pytest-cov, generates HTML and XML reports, uploads them as artifacts, and displays coverage metrics. A coverage badge is now shown in README.md alongside other workflow badges.
 
 # 0.14.0 (2025-12-14)