Address review feedback: Add logger caching, improve error handling, expand tests

- Cache litellm logger instance globally for performance optimization
- Implement more specific warning pattern filtering instead of broad matching
- Add robust error handling with graceful degradation in suppression
- Enhance streaming error handling with better logging and continue logic
- Add 3 new comprehensive tests:
  - test_concurrent_llm_calls: Verify thread safety with concurrent LLM calls
  - test_logger_caching_performance: Confirm logger instance caching works
  - test_suppression_error_handling: Test graceful degradation on logger errors
- Fix all lint errors (unused imports) in test file

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

tests/test_sys_stream_hijacking.py

@@ -2,7 +2,8 @@
 
 import sys
 import io
-from unittest.mock import patch
+from unittest.mock import patch, MagicMock
+import pytest
 
 
 def test_crewai_hijacks_sys_streams():
@@ -10,7 +11,7 @@ def test_crewai_hijacks_sys_streams():
     original_stdout = sys.stdout
     original_stderr = sys.stderr
     
-    import crewai.llm
+    import crewai.llm  # noqa: F401
     
     try:
         assert sys.stdout is not original_stdout, "sys.stdout should be hijacked by FilteredStream"
@@ -24,7 +25,7 @@ def test_crewai_hijacks_sys_streams():
 
 def test_litellm_output_is_filtered():
     """Test that litellm-related output is currently filtered (before fix)."""
-    import crewai.llm
+    import crewai.llm  # noqa: F401
     
     captured_output = io.StringIO()
     
@@ -51,7 +52,7 @@ def test_litellm_output_is_filtered():
 
 def test_normal_output_passes_through():
     """Test that normal output passes through correctly after the fix."""
-    import crewai.llm
+    import crewai.llm  # noqa: F401
     
     captured_output = io.StringIO()
     original_stdout = sys.stdout
@@ -76,7 +77,7 @@ def test_crewai_does_not_hijack_sys_streams_after_fix():
         if 'crewai' in sys.modules:
             del sys.modules['crewai']
     
-    import crewai.llm
+    import crewai.llm  # noqa: F401
     
     assert sys.stdout is original_stdout, "sys.stdout should NOT be hijacked after fix"
     assert sys.stderr is original_stderr, "sys.stderr should NOT be hijacked after fix"
@@ -104,3 +105,66 @@ def test_litellm_output_still_suppressed_during_llm_calls():
             
             output = captured_stdout.getvalue() + captured_stderr.getvalue()
             assert "litellm" not in output.lower(), "litellm output should still be suppressed during calls"
+
+
+def test_concurrent_llm_calls():
+    """Test that contextual suppression works correctly with concurrent calls."""
+    import threading
+    from crewai.llm import LLM
+    
+    results = []
+    
+    def make_llm_call():
+        with patch('litellm.completion') as mock_completion:
+            mock_completion.return_value = type('MockResponse', (), {
+                'choices': [type('MockChoice', (), {
+                    'message': type('MockMessage', (), {'content': 'test response'})()
+                })()]
+            })()
+            
+            llm = LLM(model="gpt-4")
+            result = llm.call([{"role": "user", "content": "test"}])
+            results.append(result)
+    
+    threads = [threading.Thread(target=make_llm_call) for _ in range(3)]
+    for thread in threads:
+        thread.start()
+    for thread in threads:
+        thread.join()
+        
+    assert len(results) == 3
+    assert all("test response" in result for result in results)
+
+
+def test_logger_caching_performance():
+    """Test that logger instance is cached for performance."""
+    from crewai.llm import suppress_litellm_output
+    
+    with patch('logging.getLogger') as mock_get_logger:
+        mock_logger = MagicMock()
+        mock_get_logger.return_value = mock_logger
+        
+        with suppress_litellm_output():
+            pass
+        
+        with suppress_litellm_output():
+            pass
+            
+        mock_get_logger.assert_called_once_with("litellm")
+
+
+def test_suppression_error_handling():
+    """Test that suppression continues even if logger operations fail."""
+    from crewai.llm import suppress_litellm_output
+    
+    with patch('logging.getLogger') as mock_get_logger:
+        mock_logger = MagicMock()
+        mock_logger.setLevel.side_effect = Exception("Logger error")
+        mock_get_logger.return_value = mock_logger
+        
+        try:
+            with suppress_litellm_output():
+                result = "operation completed"
+            assert result == "operation completed"
+        except Exception:
+            pytest.fail("Suppression should not fail even if logger operations fail")