Fix fake mode detection

[angelayi]

Differential Revision: D87577206

[pytorch-bot]

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❌ 2 New Failures

As of commit d1e0727 with merge base 33ec615 ():

NEW FAILURES - The following jobs have failed:

• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 255
• Test CUDA Builds / test-models-cuda (conv1d) / linux-job (gh)
  RuntimeError: Command docker exec -t 5d651dca588a0eebfee81ff0d6076b8a53bda02359d2453f632ba31b06f2a639 /exec failed with exit code 1

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[Copilot]

Pull Request Overview

This PR fixes the fake mode detection in the lift_constant_tensor_pass function by using the more robust _detect_fake_mode_from_gm utility function instead of directly accessing the fake mode from the first node's metadata. This addresses a known issue where the first node may not always have the expected metadata structure, particularly when the first node is a scalar.

• Replaces brittle metadata access with a dedicated utility function
• Imports _detect_fake_mode_from_gm from torch._export.utils
• Adds a blank line for better code formatting

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Pull request overview

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[zingo]

Hi this might have broken something in the Cortex-M backend.
https://hud.pytorch.org/hud/pytorch/executorch/main/1?per_page=50&name_filter=cortex-m
@oscarandersson8218 has a fix ongoing that will remove the Cortex-M scalar tests from add and mul ops as they don't make sense.