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/models.py

@@ -85,6 +85,16 @@ class MarkdownGenerationResult(BaseModel):
     fit_markdown: Optional[str] = None
     fit_html: Optional[str] = None
 
+@dataclass
+class TraversalStats:
+    """Statistics for the traversal process"""
+
+    start_time: datetime = datetime.now()
+    urls_processed: int = 0
+    urls_failed: int = 0
+    urls_skipped: int = 0
+    total_depth_reached: int = 0
+    current_depth: int = 0
 
 class DispatchResult(BaseModel):
     task_id: str