Currently, for iterators that can be used both as inputs and output of algorithms, we provide distinct types in cccl.parallel:

• ReverseInputIterator
• ReverseOutputIterator
• TransformIterator
• TransformOutputIterator
• ZipIterator ( currently we support input only, but could be an output iterator as well)

It would be good to unify these so that a ReverseIterator/TransformIterator/ZipIterator could be used either as an input or an output.

For iterators like CountingIterator where maybe it doesn't make sense to use as an output iterator, an algorithm should raise if provided as an output iterator.