[cpu][ci] Add CPU Attention Tests for Neon Backend

[fadara01]

Purpose

Add CPU Attention Tests for Neon Backend
Should really have been part of #29193 but I missed it

Test Plan

Arm CI which includes CPU attention tests.

Test Result

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Essential Elements of an Effective PR Description Checklist

• [Y] The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• [Y] The test plan, such as providing test command.
• [Y] The test results, such as pasting the results comparison before and after, or e2e results
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[gemini-code-assist]

Code Review

This pull request adds CPU attention tests for the Neon backend, which is a good addition for ensuring correctness on ARM platforms. The changes include a new test case specifically for Neon and modifications to existing tests to dynamically select the appropriate instruction set architecture (ISA).

My review identified two critical issues in the implementation of these tests. First, a new helper function get_attn_isa contains a latent bug that would cause a TypeError if called with an argument. Second, the new Neon-specific test has an incorrect skipif condition, causing it to be skipped on the intended ARM hardware and run on other platforms where it is not applicable. I've provided suggestions to fix both issues to ensure the tests function as intended.

[fadara01]

Arm CI running here: https://buildkite.com/vllm/ci/builds/42661/steps/canvas?sid=019b03c0-6499-425b-b296-f762a9b2add3

[fadara01]

@mgoin / @bigPYJ1151 could you guys have a look?

[mergify]

Hi @fadara01, the pre-commit checks have failed. Please run:

uv pip install pre-commit
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

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Tip

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