[ExecuTorch][llm] Wire --use_moe_quantized_op through export pipeline and LLM config

[digantdesai]

Stack from ghstack (oldest at bottom):

• -> [ExecuTorch][llm] Wire --use_moe_quantized_op through export pipeline and LLM config #21126
• [ExecuTorch][llm] Add MoE quantized custom op documentation #21125
• [ExecuTorch][llm] Fuse w1+w3 into single GEMM in quantized_moe_ffn #21124
• [ExecuTorch][llm] Add numerical kernel tests for quantized_moe_ffn #21123
• [ExecuTorch][llm] Add source-transform and Meta-kernel tests for MoE op #21122
• [ExecuTorch][llm] Add MoE source transformation with INT4 quantized packing #21121
• [ExecuTorch][llm] Add Meta kernel and registration probe for quantized_moe_ffn #21120
• [ExecuTorch][llm] Add quantized_moe_ffn custom op with C++ kernel #21119

Add --use_moe_quantized_op to the argparse and LLM configuration paths, thread it through _get_source_transforms. The transform replaces eager MoE modules once through the common export pipeline and preserves shared-expert behavior.

Differential Revision: D102381996

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21126

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure, 1 Unrelated Failure, 1 Unclassified Failure

As of commit 91e8c0a with merge base bfed808 ():

NEW FAILURE - The following job has failed:

• pull / unittest-buck / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 455aafa8daa737b08176476e24bbaf8c2c9b717077fe1b7d16578e2f07755513 /exec failed with exit code 3

UNCLASSIFIED FAILURE - DrCI could not classify the following job because the workflow did not run on the merge base. The failure may be pre-existing on trunk or introduced by this PR:

• MLX / test-mlx-qwen35-moe / test-mlx-qwen35-moe (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  examples/models/qwen3_5_moe/test_chunked_prefill.py::TestChunkedPrefill::test_chunked_prefill_matches_unchunked

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest-buck / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 3

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[github-actions]

This PR needs a release notes: label

If your change should be included in the release notes (i.e. would users of this library care about this change?), please use a label starting with release notes:. This helps us keep track and include your important work in the next release notes.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "release notes: none"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.