Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

tests/unit/test_settings_routes.py

@@ -42,7 +42,7 @@ def test_update_css_settings_persists_changes(
 
 @pytest.mark.usefixtures("db_session")
 def test_update_css_settings_invalid_value_returns_422(
-    api_client: TestClient
+    api_client: TestClient,
 ) -> None:
     response = api_client.put(
         "/api/settings/css",