ci: lint and enforce linting (#829)

@eddyxu added instructions for linting here:

7af213801a/python/README.md (L45-L50)

However, we had a lot of failures and weren't checking this in CI. This
PR fixes all lints and adds a check to CI to keep us in compliance with
the lints.

.github/workflows/python.yml

@@ -38,8 +38,10 @@ jobs:
         pip install -e .[tests]
         pip install tantivy@git+https://github.com/quickwit-oss/tantivy-py#164adc87e1a033117001cf70e38c82a53014d985
         pip install pytest pytest-mock ruff
-    - name: Lint
+    - name: Format check
       run: ruff format --check .
+    - name: Lint
+      run: ruff .
     - name: Run tests
       run: pytest -m "not slow" -x -v --durations=30 tests
     - name: doctest