Go backend:
- Add AudioCodec field to DownloadResult and DownloadResponse
- Extension download results can now include audio_codec/audioCodec
- ffmpegGetInfo and probeAudioQuality now return codec field
- Add trackItemBytes option to file.download() for custom progress handling
Flutter:
- Check audio_codec before container conversion
- Skip FLAC conversion if source codec is lossy (AAC, MP3, Opus, etc.)
- Prevents fake upscale from lossy to lossless containers