feat: Add virtual scroll support for modern web scraping

Add comprehensive virtual scroll handling to capture all content from pages that use DOM recycling techniques (Twitter, Instagram, etc).

Key features:
- New VirtualScrollConfig class for configuring virtual scroll behavior
- Automatic detection of three scrolling scenarios: no change, content appended, content replaced
- Intelligent HTML chunk capture and merging with deduplication
- 100% content capture from virtual scroll pages
- Seamless integration with existing extraction strategies
- JavaScript-based detection and capture for performance
- Tree-based DOM merging with text-based deduplication

Documentation:
- Comprehensive guide at docs/md_v2/advanced/virtual-scroll.md
- API reference updates in parameters.md and page-interaction.md
- Blog article explaining the solution and techniques
- Complete examples with local test server

Testing:
- Full test suite achieving 100% capture of 1000 items
- Examples for Twitter timeline, Instagram grid scenarios
- Local test server with different scrolling behaviors

This enables scraping of modern websites that were previously impossible to fully capture with traditional scrolling techniques.

crawl4ai/__init__.py

@@ -2,8 +2,8 @@
 import warnings
 
 from .async_webcrawler import AsyncWebCrawler, CacheMode
-# MODIFIED: Add SeedingConfig here
-from .async_configs import BrowserConfig, CrawlerRunConfig, HTTPCrawlerConfig, LLMConfig, ProxyConfig, GeolocationConfig, SeedingConfig
+# MODIFIED: Add SeedingConfig and VirtualScrollConfig here
+from .async_configs import BrowserConfig, CrawlerRunConfig, HTTPCrawlerConfig, LLMConfig, ProxyConfig, GeolocationConfig, SeedingConfig, VirtualScrollConfig
 
 from .content_scraping_strategy import (
     ContentScrapingStrategy,
@@ -92,8 +92,9 @@ __all__ = [
     "BrowserProfiler",
     "LLMConfig",
     "GeolocationConfig",
-    # NEW: Add SeedingConfig
+    # NEW: Add SeedingConfig and VirtualScrollConfig
     "SeedingConfig",
+    "VirtualScrollConfig",
     # NEW: Add AsyncUrlSeeder
     "AsyncUrlSeeder",
     "DeepCrawlStrategy",