Switch to crawl4ai async to fix issues with webcrawler

[dirkbrnd]

Description

Fixes #1556

Crawl4ai has deprecated their synchronous webcrawler. This switches to using the AsyncWebCrawler.

In future when we support async tool calling, we can use it more directly.

** This works best with crawl4ai>=0.4.1 **

Fixes # (issue)

Type of change

Please check the options that are relevant:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Model update
• Infrastructure change

Checklist

• My code follows Phidata's style guidelines and best practices
• I have performed a self-review of my code
• I have added docstrings and comments for complex logic
• My changes generate no new warnings or errors
• I have added cookbook examples for my new addition (if needed)
• I have updated requirements.txt/pyproject.toml (if needed)
• I have verified my changes in a clean environment