fix: clean up type annotations and unused imports

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_proxy.py

@@ -1,8 +1,4 @@
-import threading
-import http.client
-import time
 import pytest
-from unittest.mock import MagicMock, patch
 from jianda_proxy.proxy import create_server