Add Bilibili SponsorBlock support

[zyhclh]

Summary

• Add a Bilibili SponsorBlock preference and fetch skip segments from the bsbsb.top API.
• Pass skip segments to the bundled IINA danmaku plugin and skip on the original playback timeline instead of cutting the media URL.
• Add in-player undo handling with a toast, keyboard shortcut, and input fallback for the overlay.

Validation

• Built successfully with xcodebuild -quiet -project IINA+.xcodeproj -scheme IINA+ -configuration Debug -derivedDataPath /private/tmp/iina-plus-derived build.
• Tested the sample Bilibili video locally in IINA+: skip works, keyboard undo works, click undo works, and undo no longer immediately re-skips the same segment.