Arm backend: Add 16A8W support and test for mul operation

[Ninja91]

Stack from ghstack (oldest at bottom):

• (to be filled)

Add 16A8W quantization support and test for the mul operation in ExecutorTorch ARM backend.

This follows the pattern established for linear operations, extending int16 support to mul operations.

Changes:

• Add INT16 dtype validation support in op_mul.py
• Add test_mul_tensor_16a8w_tosa_INT test function
• Enable test_mul.py in test targets configuration

The 16A8W configuration uses 16-bit activations with 8-bit weights, enabling higher precision for activations while maintaining weight efficiency.

Differential Revision: D80510628

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 3 New Failures

As of commit 11571f9 with merge base 9053089 ():

NEW FAILURES - The following jobs have failed:

• Propose to merge ghstack orig PRs to main / Try to create a PR with ghstack /orig branch (gh)
  Process completed with exit code 1.
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  backends/arm/test/models/stable_diffusion/test_T5EncoderModel.py::TestT5EncoderModel::test_T5EncoderModel_tosa_MI
• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  RuntimeError: Command docker exec -t 8f72fa47243362514b9645b9db022b2b1c58491ad9be99eb6310bb266ebb43d1 /exec failed with exit code 1

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[github-actions]

Looks like this PR hasn't been updated in a while so we're going to go ahead and mark this as Stale.
Feel free to remove the Stale label if you feel this was a mistake.
If you are unable to remove the Stale label please contact a maintainer in order to do so.
If you want the bot to never mark this PR stale again, add the no-stale label.
Stale pull requests will automatically be closed after 30 days of inactivity.

[zingo]

Is this still needed?

[zingo]

We think this is done and can be closed, please reopen of you don't agree.