Function walk_dir_linear 

pub async fn walk_dir_linear<Func, Fut, E>(
    path: impl AsRef<Path>,
    entry_function: Func,
) -> Result<Result<(), E>>
where
    Func: FnMut(DirEntry) -> Fut,
    Fut: Future<Output = Result<(), E>>,

Walk directories linearly.

If an error occurs it’ll propagate the main function.