Arm backend: Fix TOSA 1.0 node visitor for sum

[per]

Summary

Fixes serialization for sum.dim_IntList node visitor as well as some rescale handling issues.

Test plan

Tested with internal and external CI.

cc @digantdesai @freddan80 @zingo @oscarandersson8218

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/10908

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 24acdb2 with merge base d069d65 ():

NEW FAILURES - The following jobs have failed:

• Apple / build-demo-ios / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 1
• pull / test-models-linux (mobilebert, xnnpack-quantization-delegation, linux.2xlarge) / linux-job (gh)
  RuntimeError: Command docker exec -t 31a6db3544b8a121a51993fdc6ff449361def4cff550e615007d9a2bfb9af3a6 /exec failed with exit code 2

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

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

• pull / test-llava-runner-linux / linux-job (gh) (trunk failure)
  test_llava_export

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