Cortex-M: add opt-in explicit layout lowering

[rascani]

Thread an experimental explicit-layout mode through the shared Edge compile
configuration, AOT compiler, quantizer, tester, and pass manager while retaining
legacy dim-order export as the default.

Explicit mode disables dim-order operators, converts Conv1d through the common
transform, runs the common channels-last pipeline, lowers anchors to the fixed
_nhwc schemas, and lowers surviving boundaries to cortex_m transpose. Output
dequantization remains a layout barrier, and unequal-shape add or multiply stays
outside the region until separately admitted.

Remove identity clones once qparams are folded, so explicit mode does not need a
second clone operator in the selective build. The pass has to run after folding:
removing clones first changes the quantize topology the fold matches and splits
the layout region in two.

Package the host test harness and assert expected Cortex-M targets before
planned-memory comparisons.

Local Corstone-300 run of the full Cortex-M suite, the common-transform suites,
and lintrunner. Not run on Cortex-M33.

Authored with Codex.

[rascani]

Stack from ghstack (oldest at bottom):

• Cortex-M: add an opt-in NHWC method I/O contract #22029
• Cortex-M: keep NHWC channel broadcasts quantized #21968
• -> Cortex-M: add opt-in explicit layout lowering #21967
• Cortex-M: make quantized add and multiply layout-agnostic #21966
• Cortex-M: add a contiguous-layout pad operator #22028
• Cortex-M: add explicit-NHWC runtime operators #21965
• Cortex-M: share layout-aware CMSIS-NN kernels #21964
• Channels last: add the common layout pipeline #21963
• Channels last: absorb boundary layout copies into the method contract #22034
• Channels last: optimize structural layout regions #21962
• Channels last: teach the data-movement passes both permute dialects #22003

[pytorch-bot]

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❌ 1 New Failure, 9 Unrelated Failures, 1 Unclassified Failure

As of commit 83ec2a7 with merge base 8b93850 ():

NEW FAILURE - The following job has failed:

• Apple / build-frameworks-ios / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1

UNCLASSIFIED FAILURE - DrCI could not classify the following job because the workflow did not run on the merge base. The failure may be pre-existing on trunk or introduced by this PR:

• trunk / test-models-macos-cpu (llama3_2_vision_encoder, portable) / macos-job (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  torchaudio

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

• pull / unittest / linux / linux-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest / macos / macos-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest / windows / windows-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• trunk / unittest-release / linux / linux-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• trunk / unittest-release / macos / macos-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions
• trunk / unittest-release / windows / windows-job (gh) (trunk failure)
  .ci/scripts/tests/test_filter_cuda_matrix.py::TestPublishedSets::test_published_python_versions

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