[EZ] Make weight_int4pack_mm compilable for half input dtype

[malfet]

To enable efficient int4 quantization on ARM

Followup after #124022

[pytorch-bot]

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✅ You can merge normally! (1 Unrelated Failure)

As of commit 66543bd with merge base ff1e3ff ():

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / linux-focal-cuda12.1-py3.10-gcc9 / test (default, 3, 5, linux.4xlarge.nvidia.gpu) (gh)
  test_foreach.py::TestForeachCUDA::test_binary_op_list_error_cases__foreach_add_cuda_bfloat16

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[mikekgfb]

Thank you!

[mikekgfb]

@pytorchbot merge

[pytorchmergebot]

Merge failed

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[malfet]

@pytorchbot merge

[pytorchmergebot]

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