Fix remaining TestGenRequest reference in format_response method

Fixed NameError that was causing Docker container crashes:
- Updated type annotation in format_response method from TestGenRequest to TestGenerationRequest
- This was the last missing reference from the class rename

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tools/testgen.py

@@ -418,7 +418,7 @@ class TestGenerationTool(BaseTool):
 
         return full_prompt
 
-    def format_response(self, response: str, request: TestGenRequest, model_info: Optional[dict] = None) -> str:
+    def format_response(self, response: str, request: TestGenerationRequest, model_info: Optional[dict] = None) -> str:
         """
         Format the test generation response.