Add tests for PlaywrightCrawler's `infinity_scroll` and `block_requests` features

Test coverage for `src/crawlee/crawlers/_playwright/_utils.py` is currently only 13%, making it the lowest-covered module in the project. This module appears to be the only one without any dedicated tests, and the functions `infinite_scrolling` and block_requests` are not tested at all (they are public functions exposed via crawling context).

Add tests to ensure these util functions are covered.
