[ENHANCEMENT]: Allow conversion between cuco::extent and cuda::std::extent

[sleeepyjack]

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

Introduction of cuda::std::span allows us to move away from the old-school but footgunny raw pointer + size interface.
cuda::std::span allows for passing a cuda::std::extent for the size of the span which can be either a runtime or compile time value.

This is similar to our cuco::extent implementation, with the only difference that the cuco:: version allows for customizing the size type (for performance reasons) while the cuda::std:: implementation always uses size_t.

To make handling of span in cuco easier, it would be nice to be able to easily convert a cuco::extent to a cuda::std::extent.

Describe the solution you'd like

Implement a conversion operator that maps cuco::extent<SizeType, Size> -> cuda::std::extent<Size>.
For the inverse case cuda::std::extent<Size> -> cuco::extent<size_t, Size> there's the caveat that we can only use size_t as the size type.

Describe alternatives you've considered

Travel back in time and standardize std::extent<Size = dynamic_extent, SizeType = size_t> ;)

Additional context

No response