feat: Enhance crawler flexibility and LLM extraction capabilities

- Add browser type selection (Chromium, Firefox, WebKit)
- Implement iframe content extraction
- Improve image processing and dimension updates
- Add custom headers support in AsyncPlaywrightCrawlerStrategy
- Enhance delayed content retrieval with new parameter
- Optimize HTML sanitization and Markdown conversion
- Update examples in quickstart_async.py for new features

.gitignore

@@ -203,4 +203,5 @@ git_changes.py
 git_changes.md
 pypi_build.sh
 
-.tests/
+.tests/
+git_changes.py