fix(cache): non-destructive backup restore, playback stability, and crash prevention

[drkvenom786]

Overview

This PR delivers non-destructive cache backup & restore merging, playback stability enhancements, and crash prevention fixes.

Key Changes

1. Non-Destructive Cache Restore:

   • Backup archives are now extracted into an isolated temporary folder before merging.
   • Preserves the device's active .uid file in exoplayer/ and download/ so ExoPlayer never treats existing chunk files as unindexed orphans on startup.
   • Maps restored chunk IDs dynamically using (maxExistingId + 1) for new tracks, or reuses the existing chunk ID if the track is already cached.
   • Restored and existing cache entries are integrated directly into the active ExoPlayerCacheIndex<activeHexUid> table, completely eliminating cache loss upon restoring.
   • Room database entries (songs, formats, artists) and restored_cache_ids.json are merged cleanly.

2. Playback Stalling & Chunk Cache Fix:

   • Fixed cache verification in MusicService.kt and DownloadUtil.kt to only check the requested dataSpec.position. Previously checking position 0L caused downstream chunks (e.g. 512KB+) to be misidentified as cached, causing playback to pause or stop after 15–30 seconds.

3. Crash Prevention (IllegalArgumentException: Out of range):

   • Wrapped the player passed to MediaLibrarySession in a ForwardingPlayer that safely clamps getBufferedPercentage() within [0, 100]. This eliminates the IllegalArgumentException: Out of range: -2524730863225 crash when buffering or playing edge-case tracks.
   • Ensured crossfade player swaps also use the safe session player wrapper.

4. Listen Time Integrity:

   • Removed artificial playback Event logging during cache restoration, preventing listening time inflation.