[FEA]: internally __restrict__ qualified `cuda::std::span`

### 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

libcu++

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

In order to improve the aliasing analysis phase, pointers should in general be `__restrict__` qualified. Unfortunately, `std::span` and its libcu++ counterpart `cuda::std::span` are obstacles to having `__restrict__` qualified pointers.

### Describe the solution you'd like

An additional parameter or some kind of template tag that internally qualifies the `cuda::std::span` pointer with `__restrict__`.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_