Scriptify mel spectrogram processor

[jackzhxng]

Example usage:

python -m executorch.extension.audio.mel_spectrogram --feature_size 128 --output_file voxtral_preprocessor.pte

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13961

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❌ 5 New Failures, 15 Pending

As of commit 471eccb with merge base 010e68a ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
• pull / test-vulkan-operators-linux / linux-job (gh)
  RuntimeError: Command docker exec -t d87c793fc2fffef3450259a10efb9e76f43d9e434a37cb672237df4d49893a26 /exec failed with exit code 127
• pull / unittest / windows / windows-job (gh)
  Process completed with exit code 1.
• pull / unittest-editable / windows / windows-job (gh)
  Process completed with exit code 1.
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 43d1fdf20360cdf04620f00cc8d4c0f3b19816068443a439ee7d229b46e2a6e6 /exec failed with exit code 1

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