[ET-VK][ez] Use tree reduction in q8ta_linear_gemv shader

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][testing] Add GPU device name override for on-device model tests #17795
• [ET-VK][qconv] Add dynamic PACKED_INT8_CONV2D memory layout for device-adaptive conv2d #17794
• [ET-VK][qconv] Enable im2col to handle grouped convolution #17793
• -> [ET-VK][ez] Use tree reduction in q8ta_linear_gemv shader #17792

Replace the serial O(WGS) reduction loop with a tree reduction pattern
(O(log2(WGS))). Previously, only thread 0 summed all 64 partial
accumulators sequentially. Now all threads participate in a classic
halving reduction, matching the pattern already used in
linear_q4gsw_coop.glsl.

Authored by Claude.

Differential Revision: D94949137

[pytorch-bot]

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❌ 15 New Failures, 1 Cancelled Job, 2 Unrelated Failures

As of commit a1e2aa2 with merge base ae41854 ():

NEW FAILURES - The following jobs have failed:

• Build Presets / linux (linux, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
• Build Presets / linux (llm, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
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• Build Presets / linux (pybind, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
• pull / test-coreml-bc-macos (macos-m2-stable) / macos-job (gh)
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• pull / test-models-linux-basic (vit, xnnpack-quantization-delegation, cmake, linux.arm64.2xlarge, execut... / linux-job (gh)
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• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-3B-2507, non-quantized) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D704:269D57:10F95B:1471C4:69A5FB32)
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-3B-2507, quantized-int4-metal) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D6BF:3CC34C:1084D7:13FDBF:69A5FB32)
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-4B-Realtime-2602, quantized-int4-metal) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D6F7:2E3025:101143:1389E8:69A5FB2E)
• Test Metal Backend / export-model-metal-artifact (nvidia, parakeet-tdt, quantized-int4-metal) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D923:193E62:FB592:132EF9:69A5FB2E)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-large-v3-turbo, non-quantized) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D92F:3CC34C:1084D9:13FDC2:69A5FB32)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-large-v3-turbo, quantized-int4-metal) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (EEB2:381148:1002C2:135C71:69A5FB2E)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-small, non-quantized) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D6B4:1856C:10A671:141D5D:69A5FB2E)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-small, quantized-int4-metal) / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (EEBE:2CA45F:1157F5:14D08A:69A5FB32)
• Test Metal Backend / test-executorch-metal-build / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D4A5:1A09F5:FE5D0:13601F:69A5FB32)
• Test Metal Backend / test-metal-backend-modules / macos-job (gh)
  An action could not be found at the URI 'https://api.github.com/repos/actions/checkout/tarball/11bd71901bbe5b1630ceea73d27597364c9af683' (D499:3CADF7:10F800:147022:69A5FB2E)

CANCELLED JOB - The following job was cancelled. Please retry:

• Check Labels (gh)

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

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

• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (mistralai, Voxtral-Mini-3B-2507, non-quantized) / windows-job (gh) (trunk failure)
  Process completed with exit code 1.
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-weight-only) / windows-job (gh) (trunk failure)
  Process completed with exit code 1.

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