Refactor test cases for improved readability and consistency

- Added blank lines for better separation of test cases in multiple test files.
- Reformatted event handling in tests for clarity and consistency.
- Ensured consistent use of multi-line formatting for dictionary arguments in event handling.
- Improved assertions and test descriptions for better understanding.
- Updated test cases across various modules including test_stream_state, test_stream_utils, test_summarization, test_thread_selector, test_tool_error_handler, test_tui_widgets, test_ui_runtime, and test_wechat_channel.

tests/test_tool_error_handler.py

@@ -16,6 +16,7 @@ from EvoScientist.middleware.tool_error_handler import (
 # Helpers
 # ---------------------------------------------------------------------------
 
+
 def _make_request(tool_name: str = "my_mcp_tool", call_id: str = "tc_001"):
     """Create a minimal ToolCallRequest-like object."""
     req = MagicMock()
@@ -152,6 +153,7 @@ class TestWrapToolCallAsync:
     @staticmethod
     def _run(coro):
         from tests.conftest import run_async
+
         return run_async(coro)
 
     def test_success_passes_through(self):