Adopt CUDA stream compatibility accessors

[bdice]

Summary

Use the get() and sync() compatibility aliases added in RMM #2537. These spellings are shared by rmm::cuda_stream_view and cuda::stream_ref.

This preserves existing stream types and public APIs while extracting mechanical accessor updates from the broader stream migration. It is independently buildable without RMM #2372 and leaves the migration PR focused on actual type and signature changes.

This updates raw CUDA, library, kernel-launch, and legacy API boundaries throughout cuVS while preserving current stream types. Changes that require RAFT to return cuda::stream_ref remain in cuVS #2521.

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.

[bdice]

Validated this preparation branch against RMM upstream/main: the local -j0 build completed and the focused IVF-PQ test passed. The dependent migration PR #2521 has been rebased onto this branch.