Fix stale Int4Tensor assertions in gemma4_31b CUDA pipeline tests

[Gasoonjia]

Packing converts Int4Tensor weights to CudaCoalescedInt4Tensor because the CUDA int4 kernel is registered only on the coalesced type, which is intentionally not a subclass of Int4Tensor. Update test_int4_weights_preserved and test_load_converts_weights to assert CudaCoalescedInt4Tensor.

[pytorch-bot]

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❌ 4 New Failures, 2 Pending

As of commit e184a21 with merge base b47e588 ():

NEW FAILURES - The following jobs have failed:

• pull / test-qnn-models-linux (mv2) / linux-job (gh)
  RuntimeError: Command docker exec -t 46f7207dafabf94d5316861abe060e1793fe9e7100351170b66a86f7cbc42e9d /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t d83b797e41f99c344634414cd39aff245061ef2ff2329a3d5271b51e66517e42 /exec failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_resnet50_model
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (facebook, dinov2-small-imagenet1k-1-layer, non-quantized) / windows-job (gh)
  Process completed with exit code 1.

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