skip cuda operations when running qwen 3.5 moe on other backend

[Gasoonjia]

This PR makes GPU related operator cuda-backend specific, to bring metal qwen 3.5 moe ci back

[pytorch-bot]

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• Rolling out OSDC (ARC) runners on pull & trunk workflows in PyTorch main

❌ 2 New Failures, 4 Cancelled Jobs, 1 Unrelated Failure

As of commit d118b2b with merge base c48ea12 ():

NEW FAILURES - The following jobs have failed:

• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t da6b53c16097c8d8fe14407ec71ed91c17e1fc5edc9236266691eafb2eb60ff2 /exec failed with exit code 139
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv2_model

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• Check Labels (gh)
• pull / unittest / macos / macos-job (gh)
• pull / unittest-buck / macos / macos-job (gh)
• pull / unittest-editable / windows / windows-job (gh)

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / unittest / windows / windows-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.

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[JacobSzwejbka]

ifdefs ok for now can we find a better way to do this