NXP backend: Linear + BatchNorm QAT fusing

[StrycekSimon]

Summary

Adds two passes for inserting/removing simulated BatchNorm fusion for QAT training, similarly to how _fuse_conv_bn_qat adds simulated Conv+BatchNorm fusion in prepare_qat_pt2e function from TorchAO.

Test plan

Added integration tests that covers newly added implementation,

cc @robert-kalmar @JakeStevens @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16623

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❌ 1 New Failure, 2 Cancelled Jobs, 1 Unrelated Failure

As of commit 8d41a7a with merge base 7a9fb3f ():

NEW FAILURE - The following job has failed:

• Copilot code review / Cleanup artifacts (gh)
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• periodic (gh)
• pull / unittest / macos / macos-job (gh)
  ##[error]The operation was canceled.

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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