NXP backend: Use new Neutron flow for failing constant pad tests.

[MartinPavella]

Summary

In Neutron SW SDK 3.1.0, some edge cases of the constant pad operator are no longer supported by the old flow. Affected tests now use the new flow where the pad is supported.

(Only the last commit is relevant)

Test plan

Unit tests provided.

cc @robert-kalmar @JakeStevens @digantdesai

[pytorch-bot]

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❌ 1 Awaiting Approval, 2 New Failures, 2 Unrelated Failures

As of commit 065dc35 with merge base 490ec5c ():

AWAITING APPROVAL - The following workflow needs approval before CI can run:

• periodic (gh)

NEW FAILURES - The following jobs have failed:

• pull / test-qnn-buck-build-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 009c29834bef95b36ca3896bf3c9cad00cb3657cf71d6f4d69561897d7d698ea /exec failed with exit code 3
• pull / test-qnn-passes-linux / linux-job (gh)
  backends/qualcomm/tests/test_passes.py::TestPasses::test_mha_to_sha

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

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

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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