NXP backend: Enable cat with new Neutron flow.

[MartinPavella]

Summary

This PR enables the delegation of the cat operator to Neutron. The updated version has basically no restrictions, and all cases are supported.

Test plan

Unit tests provided.

cc @robert-kalmar @JakeStevens @digantdesai @rascani

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20106

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 7de1e9e with merge base 0881b22 ():

NEW FAILURES - The following jobs have failed:

• pull / test-mcu-cortex-m-backend / linux-job (gh)
  RuntimeError: Command docker exec -t 8e37d70aade4aa12e35dcd9ce15a056f78610b092ec0cf6aff27770b1eab89e2 /exec failed with exit code 1
• pull / test-sqnr-static-llm-qnn-linux (smollm2_135m) / linux-job (gh)
  RuntimeError: Command docker exec -t af37177af3e4c0ae13a2dfab9b4a6565c91034886c39b996ef29357b30a5b250 /exec failed with exit code 92

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

• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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• ❌ - login: @MartinPavella / name: Martin Pavella. The commit (29720ef, 7de1e9e) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

[MartinPavella]

@novak-vaclav, @irtrukhina please feel free to have a look.

[novak-vaclav]

Two small details, otherwise LGTM. Good job! 😊