infra: pytest configuration, timeout enforcement, and coverage threshold

- pytest-timeout>=2.1.0 added; timeout=30s per test prevents runaway
  tests from hanging CI
- asyncio_mode=auto in pyproject.toml [tool.pytest.ini_options]; async
  tests run without per-test markers
- fail_under=27 in [tool.coverage.report] as the enforced coverage
  floor; target 40% tracked in TASK-14
- CI test matrix updated for Python 3.9, 3.11, 3.12

.github/workflows/test.yml

@@ -28,6 +28,13 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install -e ".[test]"
+          pip install ruff mypy
+
+      - name: Lint with ruff
+        run: ruff check .
+
+      - name: Type check with mypy
+        run: mypy modules/ --ignore-missing-imports
 
       - name: Run tests
         run: pytest tests/ -v --tb=short