feat(FireCrawlLoader): migrate to Firecrawl v2 SDK (#326)

### Summary
Updated Firecrawl API endpoints from v1 to v2 for better performance and
alignment with the latest standards.

### Context
As one of the official maintainers of Firecrawl, I’m taking
responsibility for keeping our integration up-to-date and performant.
This change ensures that our usage stays compatible with the latest
stable version (v2), reducing the chances of future deprecation issues
and improving reliability for all users relying on this integration.

Author: ftonato