[FEA]: Guarantee monotonic-increating temp_storage_bytes (for d_temp_storage) wrt num_items

### 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

CUB

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

For many of my algorithms I will be executing a series of cub functions with varying num_items values and it is cost-prohibitive to allocate d_temp_storage each time. I cannot predict ahead-of-time what num_items will be but I can guarantee a tight bound on the max value. I currently query temp_storage_bytes with this bound value and allocate a block of memory of the queried size to use for all subsequent cub functions. This works in practice but so far as I can tell, is not formally guaranteed to work.

### Describe the solution you'd like

Guarantee that (for the same function and same template parameters), the output temp_storage_bytes value is a non-strict monotonic increasing function of num_items.

### Describe alternatives you've considered

Nvidians: don't suggest workarounds and alternative solutions before reading internal discussion on Slack cdd-cub.

### Additional context

_No response_