[FEA]: Improve and cleanup `ThreadLoad`

### 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.

`ThreadLoad` is a fundamental utility in CUB. On the other hand, it misses some key features, especially on recent GPU architectures.

### Describe the solution you'd like

Feature list:

- Cache eviction policies on recent GPU architectures (SM70+) are missing
- Cache prefetch, e.g. `.L2::256B`, is not handled
- Non-trivially copyable data types are handled incorrectly
- We don't support 32-bit platforms anymore. The following macros are not more needed `_CUB_ASM_PTR_`, `__CUB_LP64__`, `_CUB_ASM_PTR_SIZE_`
- Some template specializations of `ThreadLoad` may not be used, e.g. `ushort4`, adding overhead to the compilation
- Add assertions for `nullptr` accesses and validate the correct memory space, i.e. `global`
- Expose in the `cub::` namespace
- Add them to public documentation

### Describe alternatives you've considered

_No response_

### Additional context

_No response_