[ET-VK][conv1d] Implement height-packed pointwise conv1d operator

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][CI] Add test-vulkan-genai job for Parakeet on NVIDIA GPU runner #18335
• [ET-VK][conv1d] Route conv1d to height-packed implementations in export pipeline #18334
• [ET-VK][conv1d] Implement height-packed depthwise conv1d operator #18333
• -> [ET-VK][conv1d] Implement height-packed pointwise conv1d operator #18332

Implement a new conv1d pointwise (kernel_size=1) operator using height-packed
layout where channels are the packed dimension (WHCN dim 1). This enables
dot-product reduction over input channels: each vec4 load gives 4 consecutive
channel values, yielding 4 MACs per dot() instruction.

Uses tiled computation with the FP tile infrastructure from linear/matmul
(FPInputTile, FPWeightTile, FPOutTile, fp_accumulate_with_fp_weight) and
4OC×4IC blocked weight packing via pack_fp_linear_weight.glsl for
cache-friendly texture2d weight reads. Adaptive tile_m selection (4/2/1 rows)
based on GPU occupancy.

Thread mapping: X=OC4 tiles, Y=L tiles, Z=batch. Each thread computes
TILE_M×TILE_N4×4 output elements. Inner loop loads input tiles and packed
weight tiles, then calls fp_accumulate_with_fp_weight for tiled FMA.

Supports both buffer and texture3d storage for input/output, texture2d or
buffer for packed weights, fp32/fp16, and optional bias. Registered as
et_vk.conv1d_pw.default (standalone custom op for testing/benchmarking).

Performance on Adreno 750 (S24):

• [1,256,1024]x[512,256,1] texture f16: 908 GFLOP/s
• [1,512,2048]x[256,512,1] texture f16: 865 GFLOP/s
• [1,128,4096]x[128,128,1] texture f16: 781 GFLOP/s
• [1,256,1024]x[512,256,1] buffer f16: 491 GFLOP/s

Differential Revision: D97344092

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18332

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✅ You can merge normally! (2 Unrelated Failures)

As of commit b6f0029 with merge base 9076110 ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / unittest / windows / windows-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.

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