[FEA]: Add support for decomposer op in cuda.parallel radix_sort

### Is this a duplicate?

- [x] I confirmed there appear to be no [duplicate issues](https://github.com/NVIDIA/cccl/issues) for this request and that I agree to the [Code of Conduct](CODE_OF_CONDUCT.md)

### Area

cuda.parallel (Python)

### Is your feature request related to a problem? Please describe.

decomposer_op allows sorting custom types in radix_sort. We currently do not expose this functionality to Python

### Describe the solution you'd like

The decomposer_op API doesn't translate very well to Python, so we need to come up with a Pythonic API

### Describe alternatives you've considered

_No response_

### Additional context

_No response_