Add ruff

Author: simontoens

.github/workflows/ci.yml

@@ -11,5 +11,9 @@ jobs:
       - uses: actions/checkout@v4
       - uses: bazelbuild/setup-bazelisk@v3
       - run: pip install --user lxml
+
       - run: bazel build //...
       - run: bazel test //...
+
+      - run: pip install ruff --user lxml
+      - run: python -m ruff check src tests