[ET-VK][patterns] Fuse torchao 4-bit quantized embedding to embedding_q4gsw

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][ops] Add eq.Scalar operator #20383
• [ET-VK][ops] Add bitwise_or / logical_or operators #20382
• -> [ET-VK][patterns] Fuse torchao 4-bit quantized embedding to embedding_q4gsw #20381

TISO and other torchao-quantized models emit a torchao.dequantize_affine -> aten.embedding subgraph for their weight-only int4 quantized embedding. The existing QuantizedEmbeddingMatch only matches the quantized_decomposed.embedding_4bit.dtype fused op, so the torchao embedding never fused: its dequantize_affine const-folded to an fp32 weight, the resulting aten.embedding exceeded the buffer-element limit and fell back to CPU, and the fp32 constant bloated the serialized model.

This adds a separate TorchAOQuantizedEmbeddingMatch matcher that recognizes the torchao int4 dequantize_affine -> aten.embedding shape (qmin=-8/qmax=7, per-row group block_size [1, G]) and rewrites it to the existing et_vk.embedding_q4gsw.default op, repacking the unpacked int8 weight into the packed 4-bit layout. It asserts symmetric quantization (zero_point == 0, which the shader assumes) and guards against repacking a shared/tied weight more than once via an et_vk_embedding_q4gsw_packed meta flag. It is kept as a separate class from QuantizedEmbeddingMatch because the two dialects produce different graph shapes (one fused op vs a split dequant+gather), so a single class would only co-locate two disjoint parse paths.

On the en_US TISO backbone the embedding now delegates to Vulkan instead of falling back to CPU, and the serialized .pte drops from 418 MiB to 348 MiB.

This change was authored with Claude.

Differential Revision: D108457797

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❌ 4 New Failures, 3 Unrelated Failures

As of commit 7783e2f with merge base 23f9021 ():

NEW FAILURES - The following jobs have failed:

• pull / test-lora-multimethod-linux / linux-job (gh)
  RuntimeError: Command docker exec -t c4f7aac2225e2b5c16667774446ce1e300a4316b55142ac47525f24ab95313f2 /exec failed with exit code 1
• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t c87cb3e035002f3e0d6bf0c0dc21817e2965a9a9a1619ce4061512e396f78f9c /exec failed with exit code 1
• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 2938ed581f272064078853d25ceaa42c71a6388d532de9472665f7896ee27db5 /exec failed with exit code 1
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t b54331e192b0f28b862f59854b618312be1ad491b6d63a0009deba12a2ad2693 /exec failed with exit code 1

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

• pull / unittest-editable / macos / macos-job (gh) (similar failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

BROKEN TRUNK - The following jobs failed but was present on the merge base:

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

• pull / test-llama-runner-qnn-linux (fp32, qnn_16a16w, qnn) / linux-job (gh) (trunk failure)
• pull / unittest / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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