Re-export the Vulkan fp16 variant with rank-3 attention

Attention now folds the singleton batch into the head dim and runs as
[H, T, D] batched matmuls. The stock 4-D reshapes each become their own
materialised view dispatch on Vulkan; this drops them and is bit-identical to
the previous export on CPU.

At the published 254-token shape: 10.30 -> 8.82 ms on an Adreno 840 and
107.58 -> 97.94 ms on a Mali-G76, which is 2.32x and 3.11x XNNPACK.

vulkan/all_minilm_l6_v2_vulkan_fp16.pte

@@ -1,3 +1,3 @@
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