fix(dispatcher): adjust memory threshold and fix dispatcher initialization

- Increase memory threshold from 70% to 90% for better resource utilization
- Remove incorrect self parameter from MemoryAdaptiveDispatcher initialization

These changes improve the crawler's performance by allowing more memory usage before throttling and fix a bug in dispatcher initialization.

crawl4ai/async_webcrawler.py

@@ -772,7 +772,6 @@ class AsyncWebCrawler:
         # Create default dispatcher if none provided
         if dispatcher is None:
             dispatcher = MemoryAdaptiveDispatcher(
-                self,
                 rate_limiter=RateLimiter(
                     base_delay=(1.0, 3.0), max_delay=60.0, max_retries=3
                 ),