Fix CI failures: resolve type checker errors and test failures

- Fix type checker errors in reasoning_handler.py: handle Union[str, dict] response types
- Fix type checker error in crew_chat.py: convert final_response to string for dict
- Update test_task_callback_returns_task_output to include completion_metadata field
- Fix integration test attribute access in test_lite_agent_with_xml_extraction

Co-Authored-By: João <joao@crewai.com>

tests/task_test.py

@@ -162,6 +162,7 @@ def test_task_callback_returns_task_output():
             "name": None,
             "expected_output": "Bullet point list of 5 interesting ideas.",
             "output_format": OutputFormat.RAW,
+            "completion_metadata": None,
         }
         assert output_dict == expected_output