Improve image proxy handling and fallback

[hjiangsu]

Pull Request Description

This PR improves the current image proxy logic:

• Handles nested proxy image URLs (e.g., instance A has image proxy enabled and serves an image from instance B with image proxy enabled)
• Added ability to load image from original URL if the proxied image fails to load. This only applies to image posts.

Issue Being Fixed

Issue Number: #1904, workaround for some images in #2001

Screenshots / Recordings

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?