feat: Add Files API support with upload, list, get and delete operations

- Implement complete Files API compatible with Gemini API format
- Support resumable file uploads with chunked transfer (tested with 15MB video)
- Create file management service with database tracking
- Add file domain models and API request/response objects
- Implement file routes with proper authentication
- Use fixed API key for Files API requests (due to Google API restrictions)
- Support file state management (PROCESSING, ACTIVE, FAILED)
- Add scheduled task for automatic expired file cleanup
- Integrate seamlessly with existing key management and load balancing

app/exception/exceptions.py

@@ -76,6 +76,8 @@ class ServiceUnavailableError(APIError):
         )
 
 
+
+
 def setup_exception_handlers(app: FastAPI) -> None:
     """
     设置应用程序的异常处理器