Function check_bundle 

pub async fn check_bundle(
    bundle: &[AssetItem],
    event_tx: &Sender<LaunchEvent>,
    concurrency: u32,
) -> Result<Vec<DownloadItem>, LaunchError>

Write every CFile to disk and return a Vec<DownloadItem> for every Asset / NativeAsset that is either missing from disk or whose SHA-1 does not match the expected value.

Emits LaunchEvent::Check progress events as each file is evaluated. Up to concurrency files are checked in parallel.