refactor: improve multimodal file handling architecture

- Make crewai_files an optional dependency with graceful fallbacks
- Move file formatting from executor to LLM layer (_process_message_files)
- Add files field to LLMMessage type for cleaner message passing
- Add cache_control to Anthropic content blocks for prompt caching
- Clean up formatters: static methods for OpenAI/Gemini, proper error handling
- Remove unused ContentFormatter protocol
- Move test fixtures to lib/crewai-files/tests/fixtures
- Add Azure and Bedrock multimodal integration tests
- Fix mypy errors in crew_agent_executor.py

lib/crewai/tests/utilities/test_files.py

@@ -6,7 +6,7 @@ from pathlib import Path
 
 import pytest
 
-from crewai.files import (
+from crewai_files import (
     AudioFile,
     File,
     FileBytes,
@@ -20,7 +20,7 @@ from crewai.files import (
     normalize_input_files,
     wrap_file_source,
 )
-from crewai.files.file import detect_content_type
+from crewai_files.core.sources import detect_content_type
 
 
 class TestDetectContentType: