Arm backend: Move rescales from SUM visitor to pass

[martinlsm]

In the SUM node visitor, an INT8->INT32 RESCALE node is inserted prior to the SUM node; similarly, an INT32->INT8 RESCALE node is inserted after.

This patch moves the insertion to InsertRescaleInt32Pass. Since SUM is decomposed, insertion of RESCALE nodes should be carried out before DecomposeSumPass (which decomposes SUM into a chain of single dim SUMs). The ordering is important to avoid redundant INT8/INT32 RESCALE nodes being inserted between each SUM node in the chain after decomposition. Only one INT8->INT32 RESCALE is needed before the chain, and an INT32->INT8 after it; between the SUM nodes in the chain, the edges are already in the correct INT32 data type.

Test plan

Tests exercising the modified pass of this patch have been added to backends/arm/test/passes/test_insert_rescale_i32_pass.py.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 8 New Failures, 3 Unrelated Failures

As of commit d0c08ca with merge base 7215b88 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 2be157ba1796f62f318a43bb318f15f7cdb19d18cd8e8a4437fd9dedea1efa0a /exec failed with exit code 1
• pull / unittest / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_linear_model
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 977ef7c819f53911b1de8dce35219a2fa4a4195ffb96f28e560691d5977248c1 /exec failed with exit code 1
• Test CUDA Builds / export-gemma3-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t 4e089ba0fddfb9cc340ca0e9d1cb979c229601cee1611f8e7a53ecab185f22e1 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t 80cb28f7b17decccf3c0a7aebb5a4b3c7b05c3fba8c6187be5f69f4dee79c776 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t 55a4731eff5547a70e1ef6642eeaf3b19c5fa7de6c94f4fe4be9145be3dbaba8 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-weight-only / linux-job (gh)
  RuntimeError: Command docker exec -t 2656fec3a5a57820fe660de40076361f142b5eb2b9ff476bdf16ba210f995323 /exec failed with exit code 2
• Test Metal Backend / export-voxtral-metal-artifact / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 2

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 / linux / linux-job (gh) (trunk failure)
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
• trunk / unittest-release / linux / linux-job (gh) (trunk failure)

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[martinlsm]

@pytorchbot label ciflow/trunk

[martinlsm]

@pytorchbot label "partner: arm"