refactor(deep-crawl): reorganize deep crawling functionality into dedicated module

Restructure deep crawling code into a dedicated module with improved organization:
- Move deep crawl logic from async_deep_crawl.py to deep_crawling/
- Create separate files for BFS strategy, filters, and scorers
- Improve code organization and maintainability
- Add optimized implementations for URL filtering and scoring
- Rename DeepCrawlHandler to DeepCrawlDecorator for clarity

BREAKING CHANGE: DeepCrawlStrategy and BreadthFirstSearchStrategy imports need to be updated to new package structure

crawl4ai/__init__.py

@@ -15,8 +15,6 @@ from .extraction_strategy import (
     JsonCssExtractionStrategy,
     JsonXPathExtractionStrategy
 )
-
-from .async_deep_crawl import DeepCrawlStrategy, BreadthFirstSearchStrategy
 from .chunking_strategy import ChunkingStrategy, RegexChunking
 from .markdown_generation_strategy import DefaultMarkdownGenerator
 from .content_filter_strategy import PruningContentFilter, BM25ContentFilter, LLMContentFilter, RelevantContentFilter
@@ -33,8 +31,6 @@ from .docker_client import Crawl4aiDockerClient
 from .hub import CrawlerHub
 
 __all__ = [
-    "DeepCrawlStrategy",
-    "BreadthFirstSearchStrategy",
     "AsyncWebCrawler",
     "CrawlResult",
     "CrawlerHub",