chore: apply ruff auto-fixes and remove dead AST scripts

tests/test_token_usage.py

@@ -1,4 +1,3 @@
-import pytest
 import sys
 import os
 
@@ -10,6 +9,5 @@ import ai_client
 def test_token_usage_tracking() -> None:
  ai_client.reset_session()
  # Mock an API response with token usage
- usage = {"prompt_tokens": 100, "candidates_tokens": 50, "total_tokens": 150}
  # This would test the internal accumulator in ai_client
  pass