Refactor test files for improved readability and consistency

- Removed unnecessary blank lines and adjusted formatting in test files.
- Ensured consistent use of commas in function calls and assertions across various test cases.
- Updated import statements for better organization and clarity.
- Enhanced mock setups in tests for better isolation and reliability.
- Improved assertions to follow a consistent style for better readability.

tests/api/v1/test_player_endpoints.py

@@ -656,4 +656,4 @@ class TestPlayerEndpoints:
             json={"volume": 100},
         )
         assert response.status_code == 200
-        mock_player_service.set_volume.assert_called_with(100)
+        mock_player_service.set_volume.assert_called_with(100)