[ET-VK] Generalize constant_pad_nd to support any storage type and packed dimension

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK] Buckify parakeet #18062
• [ET-VK][qlinear] Add bias support to q4gsw and dq8ca_q4gsw quantized linear ops #18061
• [ET-VK] Implement missing Vulkan operators for Parakeet TDT model #18059
• [ET-VK] Add ANY_STORAGE support to argmax and argmin #18058
• [ET-VK] Add ANY_STORAGE support to embedding #18057
• [ET-VK] Add ANY_STORAGE support to repeat #18056
• [ET-VK] Add ANY_STORAGE support to native_layer_norm #18055
• [ET-VK] Add ANY_STORAGE support to softmax and log_softmax #18054
• [ET-VK] Add ANY_STORAGE support to expand_copy #18053
• [ET-VK] Add ANY_STORAGE support to arange and full #18052
• -> [ET-VK] Generalize constant_pad_nd to support any storage type and packed dimension #18051
• [ET-VK] Add symint infrastructure to VulkanBackend and ComputeGraph #18050
• [ET-VK] Add Vulkan backend support for Parakeet runner and export #18049
• [ET-VK][ez] Fix IndexError in Vulkan partitioner DtypeSetList/TensorRepSetList #18048
• [ET-VK] Fix exponential blowup in tag_memory_meta_pass repset tracing #18207

Replace the old pad_channel and pad_height_width shaders with generalized pad_buffer and pad_texture shaders that work with any storage type and packed dimension using BufferMetadata/TextureMetadata and indexing.glslh utilities.

Differential Revision: D95970168

[pytorch-bot]

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❌ 1 New Failure, 11 Cancelled Jobs, 1 Unrelated Failure

As of commit 9b6a027 with merge base 22174fa ():

NEW FAILURE - The following job has failed:

• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t 003ca2a5d8b44dc6685d0baf7abca1622eb88441dbc1e99ef5fdf6aff5b62c76 /exec failed with exit code 139

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-3B-2507, non-quantized) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-3B-2507, quantized-int4-metal) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-4B-Realtime-2602, quantized-int4-metal) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (nvidia, parakeet-tdt, non-quantized) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (nvidia, parakeet-tdt, quantized-int4-metal) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-large-v3-turbo, non-quantized) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-large-v3-turbo, quantized-int4-metal) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-small, non-quantized) / macos-job (gh)
• Test Metal Backend / export-model-metal-artifact (openai, whisper-small, quantized-int4-metal) / macos-job (gh)
• Test Metal Backend / test-executorch-metal-build / macos-job (gh)
• Test Metal Backend / test-metal-backend-modules / macos-job (gh)

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

• pull / test-moshi-linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/libs/libssh/libssh-gcrypt-4_0.9.6-2ubuntu0.22.04.6_amd64.deb 404 Not Found [IP: 91.189.91.81 80]

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