Arm backend: Add support for aten.slice_copy with non-unit step

[YufengShi-dudu]

• Decompose strided slice_copy into unit-step slice_copy plus optional right padding and view_copy reshapes
• Update SliceCopySupported check for the supported pattern
• Add non-unit-step slice tests

Change-Id: Ida60ee2f42c283d50c9e3185dca1f9ea2238cf83

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16872

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❌ 3 New Failures

As of commit 69a0848 with merge base 74ea584 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-deps (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 7fdd02adc34f795f873a4e526b055f27eb9b81434bc09502408f2ca2dc45518f /exec failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model
• trunk / test-mcu-cortex-m-backend / linux-job (gh)
  RuntimeError: Command docker exec -t 49baf8803f701b016d352ee89c07ff6c01aba42e9131fb8bf998a202c18a16d5 /exec failed with exit code 1

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