[ET-VK][q8ta] Add q8ta_linear_gemv op for batch-1 int8 linear

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][ez][qconv] Add auto-selection to prefer im2col for q8ta_conv2d #17568
• [ET-VK][q8ta] Fix addmm arg indexing in QuantizedLinearMatch #17567
• -> [ET-VK][q8ta] Add q8ta_linear_gemv op for batch-1 int8 linear #17566
• [ET-VK][q8ta] Add q8ta_linear operator for int8 quantized linear #17565
• [ET-VK][export] Update tensor representation sync logic to allow for flexibility in memory layouts #17564
• [ET-VK] Support different input layouts in q8ta_binary operator #17563
• [ET-VK][ez] Always partition batch norm as it will be fused #17508
• [ET-VK] Add fused q8ta_relu unary operator for int8x4 tensors #17507
• [ET-VK][qconv] Add apply_relu support to q8ta conv operators #17506
• [ET-VK][qconv] Pad weight_sums buffer to multiple-of-4 alignment #17505
• [ET-VK][qconv] Fix depthwise weight_sums sum dimension #17504

Add a cooperative GEMV variant of q8ta_linear optimized for batch size 1. The existing q8ta_linear uses a tiled algorithm with 4H4W packed int8 layout, which is inefficient for single-row inputs because it wastes 3/4 of each ivec4 block. The new q8ta_linear_gemv uses 4W packed int8 layout (scalar int[] buffers) and a cooperative algorithm where 64 threads split the K reduction dimension with shared memory tree reduction.

The shader loads one packed int32 (4 int8 values) per thread per K iteration and accumulates dot products against the weight tile using dotPacked4x8AccSatEXT. After reduction, thread 0 applies scales, zero points, bias, and quantizes the output.

The pattern matcher in quantized_linear.py selects q8ta_linear_gemv when the input batch dimension is 1, falling back to q8ta_linear for larger batches.

Also adds PACKED_INT8_4W (value 5) to the serialization schema to support the 4W memory layout in the export pipeline.

Authored with Claude.

Differential Revision: D93768643

[pytorch-bot]

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❌ 3 New Failures

As of commit a1fde3c with merge base 7b843e4 ():

NEW FAILURES - The following jobs have failed:

• pull / test-openvino-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 3196dd6edb3ca5e7b09a5aa17b72865ff2b2a4800e6f0e365ca3f2d15cfaab9b /exec failed with exit code 1
• pull / test-vulkan-operators-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 7bf4bd60097ef051570a1e3da1630c7bb688df0a10a7373e70b4a621770c10a2 /exec failed with exit code 139
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t bb72745dd36d2f34b4dbc308a9a598042f11be2ff6607002112ef3b29621403d /exec failed with exit code 1

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