[DOC]: Clarity check of CUB docs

### Is this a duplicate?

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

### Is this for new documentation, or an update to existing docs?

New

### Describe the incorrect/future/missing documentation

We receive a number of reports on documentation bugs. Some of these are caused by copy-paste. But more importantly, some of the docs are just difficult to understand. We should make a pass through CUB docs to see if we can preemptively improve clarity and fix bugs to save users some time.

### If this is a correction, please provide a link to the incorrect documentation. If this is a new documentation request, please link to where you have looked.

_No response_