Fix pillar guardrails tests for parallel execution

The setup_and_teardown fixture was failing with "ImportError: module
litellm not in sys.modules" during parallel test execution. This occurs
because another worker might have removed/modified litellm from
sys.modules before this test tries to reload it.

Fix: Check if litellm is in sys.modules before attempting reload.

tests/test_litellm/proxy/guardrails/test_pillar_guardrails.py

@@ -51,9 +51,15 @@ def setup_and_teardown():
     """
     import importlib
     import asyncio
+    import sys
 
     # Reload litellm to ensure clean state
-    importlib.reload(litellm)
+    # During parallel test execution, another worker might have removed litellm from sys.modules
+    # so we need to ensure it's imported before reloading
+    if "litellm" not in sys.modules:
+        import litellm as _litellm
+    else:
+        importlib.reload(litellm)
 
     # Set up async loop
     loop = asyncio.get_event_loop_policy().new_event_loop()