Use async memory resource by default in microbenchmarks

[vuule]

Description

Closes #23464

Changes the default --rmm_mode for the nvbench base fixture from pool to async.

Measured cases show up to 10% lower performance, with the exception of segmented_bitmask_and, which makes many allocations (10K) and get 60% slower with async mr.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[vuule]

/ok to test b98ce36

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between e9b1458 and 4bff058.

📒 Files selected for processing (1)

• cpp/benchmarks/fixture/nvbench_fixture.hpp

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📝 Walkthrough

Summary by CodeRabbit

• New Features
  • Benchmarks now default to CUDA’s asynchronous memory resource for improved memory management behavior.

Walkthrough

The NVBench fixture now documents and selects the RMM async device resource by default. The SPDX attribution also includes affiliates.

Changes

Benchmark resource default

Layer / File(s)	Summary
Align fixture documentation and default resource cpp/benchmarks/fixture/nvbench_fixture.hpp	The fixture documentation identifies the RMM async device resource as the default. nvbench_base_fixture::rmm_mode changes from "pool" to "async". The SPDX attribution includes affiliates.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: bdice, davidwendt, gregorykimball

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The change implements issue #23464 by setting the nvbench fixture default rmm_mode to async.
Out of Scope Changes check	✅ Passed	The copyright and fixture documentation updates support the requested default change and are not out of scope.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly states the primary change: using the async memory resource by default in microbenchmarks.
Description check	✅ Passed	The description directly explains the default change, performance impact, linked issue, and checklist status.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[vuule]

/ok to test 84a4d4f