test: Update tests to mock async_dispatch for asynchronous tool execution engine.

tests/test_deepseek_provider.py

@@ -1,3 +1,4 @@
+import unittest.mock
 from unittest.mock import patch, MagicMock
 from src import ai_client
 
@@ -55,7 +56,7 @@ def test_deepseek_tool_calling(mock_post: MagicMock) -> None:
     """
  ai_client.set_provider("deepseek", "deepseek-chat")
  with patch("src.ai_client._load_credentials", return_value={"deepseek": {"api_key": "test-key"}}), \
-   patch("src.mcp_client.dispatch") as mock_dispatch:
+   patch("src.mcp_client.async_dispatch", new_callable=unittest.mock.AsyncMock) as mock_dispatch:
   
   # Round 1: Model calls a tool
   mock_resp1 = MagicMock()