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/async_database.py

@@ -9,7 +9,7 @@ import json  # Added for serialization/deserialization
 from .utils import ensure_content_dirs, generate_content_hash
 from .models import CrawlResult, MarkdownGenerationResult
 import aiofiles
-from .version_manager import VersionManager
+from .utils import VersionManager
 from .async_logger import AsyncLogger
 from .utils import get_error_context, create_box_message