Arm backend: Rewrite cat->slice patterns

[oscarandersson8218]

Add RewriteCatSlicePass to rewrite static unit-stride slices along a concat dimension in terms of their overlapping original inputs.

Only rewrite complete groups of slice users when the replacement does not increase the operation count. Preserve qparams for cat's tensor-list input and void materializing no-op slices for complete inputs.

This avoids materializing an intermediate concat when only part of its result is needed.

cc @digantdesai @freddan80 @per @zingo @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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❌ 1 New Failure, 1 Unrelated Failure, 1 Unclassified Failure

As of commit aa004e1 with merge base 9e84b61 ():

NEW FAILURE - The following job has failed:

• trunk / test-cortex-m-e2e / run (mv3, cortex-m0plus) / mv3-cortex-m0plus (gh)
  RuntimeError: Command bash /__w/_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-coreml (ic3) / macos-job (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  ##[error]The operation was canceled.

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

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

• trunk / test-samsung-models-linux / linux-job (gh) (trunk failure)
  test_mobilebert_qat_a8w8

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