[FEA] Split Bitset code (#2295)

Splitting the Bitset code into a `.hpp` and `.cuh` header allow the declaration of `ann::search_with_filters` with a `bitset_filter` to be made without using CUDA code in headers.
This is useful for cuVS where the headers `ivf_pq.hpp` need to declare `search_with_filter` and stay CUDA-free.

Authors:
  - Micka (https://github.com/lowener)

Approvers:
  - Corey J. Nolet (https://github.com/cjnolet)

URL: #2295