Refactor Crawler.processPage for better maintainability

[saurabhsharma2u]

Refactored processPage method in plugins/core/src/crawler/crawler.ts into smaller helper methods (fetchPage, handleCachedResponse, handleRedirects, handleSuccessResponse) to reduce complexity and improve readability.

Note: The original task pointed to plugins/core/src/crawler/crawl.ts, but that file is now a facade for the Crawler class. The complexity described was found in Crawler.processPage within plugins/core/src/crawler/crawler.ts, so the refactoring was applied there.

Changes:

• Extracted fetchPage for network requests.
• Extracted handleCachedResponse for 304 logic.
• Extracted handleRedirects for redirect chain processing.
• Extracted handleSuccessResponse for 200 OK processing.
• Improved type safety by using FetchResult and GraphNode types instead of any.
• Preserved error handling by wrapping processPage logic in a try/catch block.

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PR created automatically by Jules for task 15433885897905652798 started by @saurabhsharma2u

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