Function player_preload_upcoming 

pub async fn player_preload_upcoming(
    player: State<'_, PlayerStateWrapper>,
    db: State<'_, DatabaseWrapper>,
    smart_cache: State<'_, SmartCacheWrapper>,
    download_manager: State<'_, DownloadManagerWrapper>,
    app: AppHandle,
    user_id: String,
    _download_base_path: String,
) -> Result<PreloadResult, String>

Preload upcoming tracks from the queue This queues background downloads for the next N tracks that aren’t already downloaded