Cortex-M backend: Update Scalar types to be int

[SaoirseARM]

Summary

• Scalar should only used if the operator truly supports either type.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16322

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❌ 2 New Failures, 1 Unrelated Failure

As of commit 5dc1aa4 with merge base cf28248 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t 1a5a78c56f23d34d89d427c992e10cd48eea626bd99d2220812472c699dc8f6f /exec failed with exit code 1
• trunk / test-arm-backend (test_pytest_models_ethosu_fvp) / linux-job (gh)
  RuntimeError: Command docker exec -t 20c044d567fd021bb8e18a9ab34b80fe73a9e3f4a48aba3e1c56110741b0fd19 /exec failed with exit code 1

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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[SaoirseARM]

@pytorchbot label "release notes: none"

[SaoirseARM]

@pytorchbot label ciflow/trunk

[SaoirseARM]

@pytorchbot label 'partner: arm'

[psiddh]

Overall LGTM, enhances the type safety!
One question though: IntArrayRef = ArrayRef<int64_t> ?

Different element sizes (4 bytes for int32_t vs 8 bytes for int64_t in IntArrayRef). Can you clarify if this change (Ln 170/ Ln 171) indeed is safe ?