refactor(scraping): replace ScrapingMode enum with strategy pattern

Replace the ScrapingMode enum with a proper strategy pattern implementation for content scraping.
This change introduces:
- New ContentScrapingStrategy abstract base class
- Concrete WebScrapingStrategy and LXMLWebScrapingStrategy implementations
- New Pydantic models for structured scraping results
- Updated documentation reflecting the new strategy-based approach

BREAKING CHANGE: ScrapingMode enum has been removed. Users should now use ContentScrapingStrategy implementations instead.

tests/test_scraping_strategy.py

@@ -0,0 +1,21 @@
+import nest_asyncio
+nest_asyncio.apply()
+
+import asyncio
+from crawl4ai import AsyncWebCrawler, CrawlerRunConfig, LXMLWebScrapingStrategy, CacheMode
+
+async def main():
+    config = CrawlerRunConfig(
+        cache_mode=CacheMode.BYPASS,
+        scraping_strategy=LXMLWebScrapingStrategy()  # Faster alternative to default BeautifulSoup
+    )
+    async with AsyncWebCrawler() as crawler:
+        result = await crawler.arun(
+            url="https://example.com", 
+            config=config
+        )
+        print(f"Success: {result.success}")
+        print(f"Markdown length: {len(result.markdown_v2.raw_markdown)}")
+
+if __name__ == "__main__":
+    asyncio.run(main())