Update screenshot handling to include customizable wait time

[RohithReddy20]

This pull request includes a small but important change to the crawl4ai/async_crawler_strategy.py file. The change involves modifying the crawl method to allow for an optional wait time before taking a screenshot.

• crawl4ai/async_crawler_strategy.py: Updated the crawl method to accept an optional screenshot_wait_time parameter, which specifies the wait time before taking a screenshot.