Bump ZINC: zolotukhin/zinc b9123c649f81

[bong-water-water-bong]

Moves third_party/zinc from c50b4add3402 to upstream main b9123c649f81.

Upstream commits (last 30):

• ac84b5de5 rocm: hipBLAS prefill attention for Gemma 4
• 34ebf0fd6 site: ROCm ahead of llama.cpp HIP in all 48 rows
• 84b8ddf06 site: re-measure Vulkan Gemma 4 26B-A4B and Qwen 3.6
• 6fc514024 vulkan: gather Gemma prefill embeddings on the GPU
• bb5be230d vulkan: record several Gemma MoE prefill layers per submission
• 6e6650b50 site: re-measure Vulkan Gemma 4 26B-A4B after the prefill changes
• 46341e40d vulkan: overlap Gemma 4's shared expert with the routed experts in prefill
• d407abaeb site: re-measure Vulkan Gemma 4 26B-A4B with the shared-expert prefill overlap
• 2125e476c tests: widen Gemma grouped MoE prefill source windows
• 25e9b81eb vulkan: record up to 16384 token-layers per Gemma MoE prefill submission
• 1926f4564 vulkan: let the Gemma MoE prefill combine overwrite instead of accumulate
• f447b5969 vulkan: batch the last layer of the Gemma MoE prefill
• cffbd6dc3 site: re-measure Vulkan Gemma 4 26B-A4B after batching the last prefill layer
• e1c1c9e05 tokenizer: merge Gemma 4 BPE by rank and always prepend BOS, like the reference
• 60c753bc7 vulkan: fix Gemma MoE prefill gate/up dropping half of every Q4_K block
• 852910afe bench: flag prompt token mismatches larger than one token
• 9c9edc03f vulkan: run the Gemma MoE prefill gate/up on DP4a with Q8_1 activations
• a2ee308e5 site: re-measure Gemma 4 on the R9700 after the tokenizer and gate/up fixes
• bd7ee7323 vulkan: chain greedy decode steps so the GPU never waits for the host
• 44d35047c vulkan: chain Muse Glimmer decode too
• cd66b9c48 site: re-measure the Vulkan tab with chained greedy decode
• d7a5ed9bf rocm: run Gemma's BLAS prefill attention in f16 on the matrix cores
• b9123c649 site: re-measure ROCm Gemma 4 with f16 prefill attention

CI here has no GPU. Before merging, on Strix Halo:
scripts/build-zinc.sh ~/.cache/zinc-pin vulkan && RADV_PERFTEST=coop_matrix ~/.cache/zinc-pin/vulkan/bin/zinc -m ~/models/Qwen3-0.6B-Q4_K_M.gguf --prompt 'The capital of France is' (first token 12095).