Major refactoring of browser strategy implementations to improve code organization and reliability:
- Move CrawlResultContainer and RunManyReturn types from async_webcrawler to models.py
- Simplify browser lifecycle management in AsyncWebCrawler
- Standardize browser strategy interface with _generate_page method
- Improve headless mode handling and browser args construction
- Clean up Docker and Playwright strategy implementations
- Fix session management and context handling across strategies
BREAKING CHANGE: Browser strategy interface has changed with new _generate_page method requirement