[ET-VK][ez] Add AOT support for PackedInt8_4C1W dtype

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][profiling] Add additional profiling blocks #17394
• [ET-VK][qconv2d][ez] Don't use im2col path for general convs #17393
• [ET-VK] Add nchw_to_int8x4_buffer shader for prepacking int8 staging data #17392
• [ET-VK] Layout-flexible impl of quantized binary #17391
• [ET-VK][ez] Make q8ta_conv2d use 4C1W layout #17390
• -> [ET-VK][ez] Add AOT support for PackedInt8_4C1W dtype #17389
• [ET-VK] Migrate to use new q8ta_conv2d ops #17388
• [ET-VK][qconv] Dynamically select between im2col path and general path #17387
• [ET-VK][qconv][ez] Make q8ta_im2col shader support stride_w != 1 #17386
• Back out "[Diff Train][pytorch/executorch] Apply fixup patch to fbsource" #17399

This adds end-to-end support for the PackedInt8_4C1W memory layout throughout the serialization and AOT pipeline. The 4C1W layout packs 4 channels into a single texel with width-major ordering, which is the natural output layout for convolutions that produce channel-packed results.

• Adds PACKED_INT8_4C1W = 8 to the FlatBuffers schema and Python schema class
• Adds deserialization mapping in VulkanBackend.cpp
• Updates quantize/dequantize per-tensor op registrations to accept any PackedInt8 layout (not just 4W4C), enabling the layout propagation pass to choose the optimal layout
• Adds new TensorRepSet constants: PACKED_INT8_BUFFER (all quantized layouts), PACKED_INT8_4C1W_BUFFER, and PACKED_INT8_CHANNELS_PACKED_BUFFER (4W4C + 4C1W)

Differential Revision: D93000167

[pytorch-bot]

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❌ 2 New Failures, 2 Unrelated Failures

As of commit 32015e1 with merge base 964c565 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_resnet50_model
• Test CUDA Builds / test-model-cuda-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t 912a0445efe356f613a1ba6f7924f531a1da8ea30ac692bc295e7c66e7d612d8 /exec failed with exit code 1

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

• periodic / test-models-linux (buck2, mv3, portable, linux.2xlarge, 90) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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

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

• pull / test-samsung-models-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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