Arm backend: Convert remaining asserts in operators to raise errors

[Sebastian-Larsson]

Asserts are converted to proper raises to ensure graph integrity.

Improve error message.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/10945

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure, 1 Pending, 1 Unrelated Failure

As of commit 782e7f9 with merge base 54e7c75 ():

NEW FAILURE - The following job has failed:

• trunk / test-llama-runner-mac (fp32, coreml) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[zingo]

failed tests are unrelated