Adopt CUDA stream compatibility accessors

[bdice]

Description

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 routing and mathematical optimization code while preserving current stream types. The remaining signature migration stays in cuOpt #1828.

Issue

rapidsai/build-planning#318

Checklist

• I am familiar with the Contributing Guidelines.
• Testing
  • New or existing tests cover these changes
  • Added tests
  • Created an issue to follow-up
  • NA
• Documentation
  • The documentation is up to date with these changes
  • Added new documentation
  • NA

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