[cuda.parallel]: cuda.parallel.iterators._iterators.IteratorBase design should support input-output iterators

The nature of the iterator is controlled by `IteratorIOKind` which only supports two modalities, `INPUT` and `OUTPUT`.

Furthermore, the iterator implementation overloads `dereference` property to provide both `dereference` and `assign` methods, thus making it impossible for `IteratorBase` to provide both.

This design needs to be fixed to support input-output iterators which `c.parallel` library supports.