Remove lock usage entirely to fix pickling issues

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

src/crewai/knowledge/source/base_file_knowledge_source.py

@@ -1,5 +1,4 @@
 import os
-import threading
 from abc import ABC, abstractmethod
 from pathlib import Path
 from typing import Dict, List, Optional, Union
@@ -30,7 +29,6 @@ class BaseFileKnowledgeSource(BaseKnowledgeSource, ABC):
     """
 
     _logger: Logger = Logger(verbose=True)
-    _lock = threading.Lock()  # Thread-safe lock for file operations
     
     file_path: Optional[Union[Path, List[Path], str, List[str]]] = Field(
         default=None,
@@ -161,12 +159,9 @@ class BaseFileKnowledgeSource(BaseKnowledgeSource, ABC):
         previously recorded timestamps to detect changes. When a file has been modified,
         it logs the change and returns True to trigger a reload.
         
-        Thread-safe: Uses a lock to prevent concurrent modifications.
-        
         Returns:
             bool: True if any file has been modified, False otherwise.
         """
-        with self._lock:
         for path in self.safe_file_paths:
             try:
                 if not path.exists():