Update fc2db scraper to handle Cloudflare and strict exceptions

[chocolate-croissant]

Scraper type(s)

• performerByName
• performerByFragment
• performerByURL
• sceneByName
• sceneByQueryFragment
• sceneByFragment
• sceneByURL
• groupByURL
• galleryByFragment
• galleryByURL
• imageByFragment
• imageByURL

Examples to test

fc2db:

• sceneByURL: https://fc2db.net/work/4925699/
• performerByURL: https://fc2db.net/actress/2559/

Short description

This PR introduces critical updates to the new fc2db scraper to handle recent changes on the target site (fc2db.net), which recently enabled Cloudflare Anti-Bot protection and custom Age Verification checks.

Key Changes:

1. FlareSolverr Integration:
   • fetch_page now detects Cloudflare challenges (403/503 or challenge text like "One moment, please...").
   • If a challenge is detected, the request is automatically routed through FlareSolverr to bypass the protection.
2. Strict Error Handling:
   • Removed the silent HTML fallback for core metadata fields (Title, Code, etc.) if the JSON-LD payload is missing.
   • Now, if the VideoObject (for scenes) or Person (for performers) JSON-LD structure is not found in the HTML response, the scraper explicitly raises a hard Exception (Failed to find JSON-LD VideoObject/Person. Cloudflare challenge may have failed, or site layout changed.).
   • This ensures the scraper fails loudly and clearly instead of silently returning partial/empty scene data (unknown -).