Expose `cub::DeviceSegmentedTopK` for arbitrary segment sizes

[elstehle]

We plan to do the heavy lifting of exposing cub::DeviceSegmentedTopK in #7616. #7616 static_asserts that users provide a static upper bound that is small enough to ensure that such a segment size could be addressed by a single thread block.

Tasks:

• Add examples for fixed large segments
• Add examples for variable segments ranging from small to large
• Remove documentation mentioning constraints on small segment sizes

Depends on:

• Design proposal: A flexible parameter and guarantees framework for (segmented) algorithms #7495
• Expose cub::DeviceSegmentedTopK for small segment sizes #7616