Fix/cue playback failure handling

[markojurkovic]

Summary

Improve failure handling for CUE and other multi-track sources so recoverable decoder behavior does not produce false track errors, while genuinely failed sources are skipped efficiently.

Changes

• Associate playback errors with the buffer chain’s originating track instead of whichever track is current when an asynchronous callback arrives.
• Ignore superseded seek failures and clear recoverable seek errors when the decoder subsequently produces valid audio.
• Treat fragment URLs as logical tracks backed by the same underlying resource.
• After an underlying resource fails to open, skip repeated decoder probes for its remaining logical tracks.
• Mark skipped tracks appropriately while searching for the next playable source.
• Publish a stream-change notification only after a fallback stream opens successfully.

Result

CUE tracks that recover from an imperfect seek are no longer incorrectly marked as failed. When a shared multi-track source genuinely cannot be opened, Cog avoids repeating the same expensive probe for every track and advances to the next playable source without presenting failed fallbacks as the current track.

Verification

• Both commits build successfully in Debug for arm64 with code signing disabled.
• git diff --check main...fix/cue-playback-failure-handling passes.

Suggested manual checks

• Play a valid multi-track CUE source and confirm recoverable seeks do not mark tracks as failed.
• Trigger rapid track transitions and confirm late errors remain attached to their originating tracks.
• Queue an unopenable multi-track source followed by a valid track.
• Confirm Cog skips the failed source without probing every logical track and begins playing the valid fallback.
• Confirm failed intermediate tracks are not briefly presented as the current stream.