Arm backend: Update weight observer for QAT

[oscarandersson8218]

Updates weight observer for QAT+per-channel. Also adds a simple test to test QAT flow.

cc @digantdesai @freddan80 @per @zingo

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14001

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❌ 4 New Failures, 1 Cancelled Job

As of commit 9f77fc2 with merge base cec1400 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  RuntimeError: Command docker exec -t 37cf3b6bcd1a6352f3ad245fc419fced4d6dbf6ccd89a0fdaddc9c8a27e86408 /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 40d5182f1aaef70f0b51f11025e0b53ce86e93e73776413d16aaf2f03ef6908b /exec failed with exit code 1
• trunk / test-arm-backend (test_pytest_ops_ethosu_fvp) / linux-job (gh)
  RuntimeError: Command docker exec -t 7bf6a43c63a547c942e5cfc497cd5622aa1f920055b2003462235d2ff7545d0e /exec failed with exit code 1
• trunk / test-models-linux-aarch64 (qwen2_5, portable, linux.arm64.2xlarge) / linux-job (gh)
  RuntimeError: Command docker exec -t 30d38d28f4e861ad3b452b2170c6ab06a08c043ae71320e3c0f09ab785e6fbf7 /exec failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• Check Labels (gh)

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[zingo]

@digantdesai this is a fix on a commet you made in #13511

[zingo]

This needed a rebase and a new PR was created due this was handled a new person (and not @oscarandersson8218 )
See #14115

This PR will be abandoned if the other PASS

[zingo]

Fixed passes working in the new PR Lets close this and use #14115