Arm backend: support torch.sum.default

[Erik-Lundell]

When sum is called without arguments,
it is traced as sum.default rather than sum.dim_IntList, which 1) is lowered to edge with dims=[] instead of None, and 2) is not annotated in the quantizer.

This commit fixes those issues and adds tests.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 8 New Failures, 2 Cancelled Jobs, 3 Unrelated Failures

As of commit fd928a6 with merge base de56c81 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 349ff4f25e79bf13ec55b708b65fbcc837e80791cfcfb344ee24781b1607262f /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 09c2abc5995dedf153005f2e26da4e543716e5eedc398b7488a9eaad0ce2d0fb /exec failed with exit code 1
• Test CUDA Builds / export-gemma3-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t f139fee82f012908ec68490f28216376a22b7f0c1557349b2421d8747915a89a /exec failed with exit code 2
• Test CUDA Builds / export-gemma3-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t 5305852578e1668c3d51e3e7ca825501edbaa20a3b0513d703f5a39b52af53f7 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-non-quantized / linux-job (gh)
  RuntimeError: Command docker exec -t 66262fe2b311f0a78a4b73557ac5b73be98a4dd006958a87f809670347bf7207 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-tile-packed / linux-job (gh)
  RuntimeError: Command docker exec -t 4dfdf098682afeeb132a1a8d3003310dcf28e635d731bda097fff5c2767a4376 /exec failed with exit code 2
• Test CUDA Builds / export-voxtral-cuda-quantized-int4-weight-only / linux-job (gh)
  RuntimeError: Command docker exec -t 43838962640d5467a7e1a6695be9ab1ca616bb4103407b90692c11cbed98845d /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

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• periodic / test-models-linux (cmake, vit, portable, linux.2xlarge, 90) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh)
  ##[error]The operation was canceled.

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

• trunk / unittest-release / linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

BROKEN TRUNK - The following jobs failed but was present on the merge base:

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

• pull / unittest / linux / linux-job (gh) (trunk failure)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)

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