[ET-VK][ops] Move group norm reduction lanes to Z

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][runtime][3/3] Enforce device-safe dispatch geometry #22225
• [ET-VK][runtime][2/3] Add typed dispatch size abstractions #22224
• [ET-VK][runtime][1/3] Prepare linear shaders for 2D dispatch #22223
• -> [ET-VK][ops] Move group norm reduction lanes to Z #22222

Move group norm's cooperative 64-thread reduction dimension from Y to Z. This preserves X as the output-element dimension while leaving Y available for two-dimensional linear dispatch wrapping.

Add an explicit null check to the resize callback while updating the implementation.

Authored with Codex.

Differential Revision: D117706347

[pytorch-bot]

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❌ 1 New Failure, 1 Unrelated Failure

As of commit 024a7e5 with merge base cf9bcd8 ():

NEW FAILURE - The following job has failed:

• Build Presets / apple (llm) / build (gh)
  ##[error]fatal: Fetched in submodule path 'extension/llm/tokenizers/third-party/json', but it did not contain e6cafa573aac6ed9227f752a5371c0b3f436307d. Direct fetching of that commit failed.

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

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

• pull / android / build-android (gh) (trunk failure)

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[shoumikhin]