Fix lint errors: Remove unused imports

- Remove unused contextlib, sys, threading, io, TextIO imports from llm.py
- Remove unused importlib import from test_sys_stream_hijacking.py
- Address Ruff lint failures from CI

Co-Authored-By: João <joao@crewai.com>

tests/test_sys_stream_hijacking.py

@@ -2,7 +2,6 @@
 
 import sys
 import io
-import importlib
 from unittest.mock import patch