Creates an iterator that lazily generates a value exactly once by invoking the provided closure.

This is commonly used to adapt a single value generator into a chain() of other kinds of iteration. Maybe you have an iterator that covers almost everything, but you need an extra special case. Maybe you have a function which works on iterators, but you only need to process one value.

Unlike once(), this function will lazily generate the value on request.

Example

auto ow = sus::iter::once_with<u16>([]() { return 3_u16; });
sus_check(ow.next().unwrap() == 3_u16);