fix(gb300): reserve TP4 aggregate memory headroom

Lower gpu-memory-utilization from 0.95 to 0.94 after TP4 aggregate c1 and c8 both ran out of memory during FP4 MoE execution.

中文：将 gpu-memory-utilization 从 0.95 降至 0.94，为 GB300 TP4 聚合式 worker 预留显存余量；此前 c1 和 c8 均在执行 FP4 MoE 时发生显存不足。

Author: ivanium

benchmarks/multi_node/srt-slurm-recipes/vllm/deepseek-v4/agentic/agg-gb300-tp4-agentic.yaml

@@ -115,7 +115,7 @@ backend:
       block-size: 256
       compilation-config: '{"cudagraph_mode":"FULL_DECODE_ONLY","mode":0}'
       max-cudagraph-capture-size: 32
-      gpu-memory-utilization: 0.95
+      gpu-memory-utilization: 0.94
       stream-interval: 10
       no-disable-hybrid-kv-cache-manager: true
       tokenizer-mode: deepseek_v4