Add test coverage reporting and pre-commit hooks (#2)

* Add test coverage reporting and pre-commit hooks

- Add pytest-cov to test dependencies, configure coverage in pyproject.toml
  (branch coverage, static asset omission, standard exclusion patterns)
- CI test job now runs with --cov and uploads coverage XML as artifact
- Add .pre-commit-config.yaml with ruff (check + format) and mypy hooks

Baseline coverage: 41% (482 tests, Python 3.13)

* Fix Copilot review: add redis dep for pre-commit mypy, explicit --cov target

- Add redis>=7.2 to mypy pre-commit hook additional_dependencies so
  mypy can resolve redis imports in isolated pre-commit environments
- Use --cov=turnstone instead of bare --cov to explicitly scope coverage

.github/workflows/ci.yml

@@ -40,4 +40,9 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
       - run: pip install -e ".[test,mq]"
-      - run: pytest tests/ -m "not live" -q
+      - run: pytest tests/ -m "not live" --cov=turnstone --cov-report=term-missing --cov-report=xml -q
+      - uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: coverage-${{ matrix.python-version }}
+          path: coverage.xml