Migrate stream APIs from rmm::cuda_stream_view to cuda::stream_ref

Summary

Track the coordinated migration of stream APIs and call sites from rmm::cuda_stream_view to CCCL's cuda::stream_ref. This propagates cuda::stream_ref through RMM containers and memory resources, RAFT resource and handle APIs, downstream C++ interfaces, Python/Cython bindings, benchmarks, tests, and documentation.

Migrations

Pass cuda::stream_ref through stream pools, resource accessors, conditionals, and downstream APIs without converting to rmm::cuda_stream_view
Use cuda::stream_ref constructions for default/legacy/per-thread streams
- rmm::cuda_stream_default ➡️ cuda::stream_ref{cudaStream_t{cudaStreamDefault}}
- rmm::cuda_stream_legacy ➡️ cuda::stream_ref{cudaStreamLegacy}
- rmm::cuda_stream_per_thread ➡️ cuda::stream_ref{cudaStreamPerThread}
Use .get() when calling an API that requires a raw cudaStream_t, including CUDA runtime, library, CUB, and legacy API boundaries (previously rmm::cuda_stream_view used value())
Use .sync() when synchronizing a cuda::stream_ref (previously rmm::cuda_stream_view used synchronize())
Update Cython declarations and call sites to pass stream references directly where supported

Preparation pull requests

These independently adopt the get() and sync() compatibility aliases from RMM #2537, reducing the migration PRs to the type and signature changes that require RMM #2372.