// AsyncLazy<T> is similar to Lazy<T>, it can store in field
// it await directly or can convert to ValueTask easily to use WhenAll.
public static AsyncLazy<T> Lazy<T>(Func<ValueTask<T>> factory)
public class AsyncLazy<T>
{
    public ValueTask<T> AsValueTask();
    public ValueTaskAwaiter<T> GetAwaiter();   
    public static implicit operator ValueTask<T>(AsyncLazy<T> source);
}