refactor(core): reorganize project structure and remove legacy code

Major reorganization of the project structure:
- Moved legacy synchronous crawler code to legacy folder
- Removed deprecated CLI and docs manager
- Consolidated version manager into utils.py
- Added CrawlerHub to __init__.py exports
- Fixed type hints in async_webcrawler.py
- Fixed minor bugs in chunking and crawler strategies

BREAKING CHANGE: Removed synchronous WebCrawler, CLI, and docs management functionality. Users should migrate to AsyncWebCrawler.

crawl4ai/chunking_strategy.py

@@ -4,7 +4,6 @@ from collections import Counter
 import string
 from .model_loader import load_nltk_punkt
 
-
 # Define the abstract base class for chunking strategies
 class ChunkingStrategy(ABC):
     """
@@ -72,6 +71,7 @@ class NlpSentenceChunking(ChunkingStrategy):
         """
         Initialize the NlpSentenceChunking object.
         """
+        from crawl4ai.le.legacy.model_loader import load_nltk_punkt
         load_nltk_punkt()
 
     def chunk(self, text: str) -> list: