ci: enhance type checking in workflow and improve test coverage

- Added a step to fail the CI if any '# type: ignore' comments are found in Python files.
- Refactored tests to use mocking for better isolation and reliability.
- Updated type hints and casting in several files to improve type safety.

.github/workflows/tests.yml

@@ -33,6 +33,14 @@ jobs:
       - name: Type check
         run: uv run ty check
 
+      - name: Fail on type: ignore (no suppressions allowed)
+        run: |
+          if grep -rE '# type: ignore|# ty: ignore' --include='*.py' . --exclude-dir=.venv --exclude-dir=.git; then
+            echo "::error::type: ignore / ty: ignore comments are not allowed. Fix the underlying type errors instead."
+            exit 1
+          fi
+          exit 0
+
       - name: Format
         run: uv run ruff format