Fix CI failures: correct context window ratio and remove unused imports

- Fix test expectations to use 0.85 ratio instead of 0.75 (matches CONTEXT_WINDOW_USAGE_RATIO)
- Remove unused imports (pytest, Mock) from test file
- Add context window size warning for large models (>100K tokens)
- Update documentation with performance considerations and rate limiting best practices
- Address code review feedback from João regarding validation and error handling

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

tests/test_aiml_api_integration.py

@@ -1,7 +1,6 @@
 """Tests for AI/ML API integration with CrewAI."""
 
-import pytest
-from unittest.mock import Mock, patch
+from unittest.mock import patch
 
 from crewai.llm import LLM
 from crewai.utilities.llm_utils import create_llm
@@ -25,7 +24,7 @@ class TestAIMLAPIIntegration:
         
         for model_name, expected_context_size in test_cases:
             llm = LLM(model=model_name)
-            expected_usable_size = int(expected_context_size * 0.75)
+            expected_usable_size = int(expected_context_size * 0.85)
             actual_context_size = llm.get_context_window_size()
             assert actual_context_size == expected_usable_size, (
                 f"Model {model_name} should have context window size {expected_usable_size}, "