asyncAndThen<U, F> method
Similar to map Except you must return a new Result.
This is useful for when you need to do a subsequent async computation using
the inner T value, but that computation might fail. Must return a ResultAsync
@param f The function that returns a ResultAsync to apply to the current
value
Implementation
@override
ResultAsync<U, F> asyncAndThen<U, F>(ResultAsync<U?, F?> Function(T t) f) =>
errAsync(this.error as F);