chore: add coverage reporting to pytest

Add `pytest-cov` to `requirements-dev.txt` and enable coverage
reporting in `run_tests.py` by including `--cov` and `--cov-
report=xml` options. This provides insight into code coverage,
helping to identify areas lacking test coverage.

Author: DefinitelyADev

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
         python run_tests.py
 
     - name: Upload coverage to Codecov
-      if: matrix.python-version == '3.11'
+      if: matrix.python-version == '3.12'
       uses: codecov/codecov-action@v5
       with:
         files: ./coverage.xml

run_tests.py

@@ -25,6 +25,8 @@ def run_tests():
             "custom_components/custom_areas/tests/",
             "-v",
             "--tb=short",
+            "--cov=custom_components/custom_areas",
+            "--cov-report=xml",
         ],
         capture_output=True,
         text=True,