Implements a new MemoryAdaptiveDispatcher class to manage concurrent crawling operations with memory monitoring and rate limiting capabilities. Changes include:
- Added RateLimitConfig dataclass for configuring rate limiting behavior
- Extended CrawlerRunConfig with dispatcher-related settings
- Refactored arun_many to use the new dispatcher system
- Added memory threshold and session permit controls
- Integrated optional progress monitoring display
BREAKING CHANGE: The arun_many method now uses MemoryAdaptiveDispatcher by default, which may affect concurrent crawling behavior
