Function trash_remote_assets_for_missing_local_files 

async fn trash_remote_assets_for_missing_local_files(
    watch_paths: &[WatchPathEntry],
    seen_paths: &HashSet<String>,
    sync_index: Arc<ShardedSyncIndex>,
    api_client: Arc<ImmichApiClient>,
)

Trash remote Immich assets when their corresponding local file has been removed.