Arm backend: Align operator_validation_utils docstrings with backend

[Sebastian-Larsson]

Use same style of docstring as in the rest of the backend.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 9 New Failures, 3 Unrelated Failures

As of commit 5a8289d with merge base f7ca57e ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t cb2ccc56659280db574640b41591af0f7b2a8dfad0771bea9fb81175fe1acd7f /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 62f6272f44da818b9b38518dcf84ea0ff6ea981ed72d5047d8d944b056e4b459 /exec failed with exit code 1
• Test CUDA Builds / export-gemma3-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t 14fb402d1e6b8c54eb9b0e00a36eb32dcf0cf41e96e3a20275620873a7ef6f7c /exec failed with exit code 2
• Test CUDA Builds / export-gemma3-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t 9bfd384707f0087e3eff7869ddb089f4affdbe2af4ade649f8422b419f15ce36 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t cc2ef0e0575cd0e27d6a9eeaf68b0c9110eff7f41b496f678585aa3ef93bc177 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t ece6a08d4fb82a9304b504e7afda444392dace763dadacb5f06c7d4c74c9de56 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-weight-only / linux-job (gh)
  RuntimeError: Command docker exec -t 88b2093b1ad602c754c733233934578775f87756add56d1c4c5e93a9b2789ea9 /exec failed with exit code 2
• Test Metal Backend / export-voxtral-metal-artifact / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 2
• trunk / unittest-release / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / unittest / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• trunk / unittest-release / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest-editable / linux / linux-job (gh) (trunk failure)

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