fix: remove expandable_segments — CoreX CUDACachingAllocator不支持

BI-V100 CoreX PyTorch的CUDACachingAllocator.cpp:545没有实现
expandable segment特性，导致模型加载阶段(VocabParallelEmbedding)
直接INTERNAL ASSERT FAILED崩溃。

替换为max_split_size_mb:512减少内存碎片化。

computility-run.yaml

@@ -48,14 +48,4 @@ env:
     - name: BI100_MOE_COREX_TOPK_SOFTMAX
       value: '1'
     - name: PYTORCH_CUDA_ALLOC_CONF
-      value: expandable_segments:True
-    - name: LD_PRELOAD
-      value: /workspace/qwen3_6_scripts/cccl_preload_allocator.so
-    - name: CCCL_ALLOC_BIN_GROWTH
-      value: '8'
-    - name: CCCL_ALLOC_MIN_BIN
-      value: '3'
-    - name: CCCL_ALLOC_MAX_BIN
-      value: '13'
-    - name: CCCL_ALLOC_MAX_CACHED_MB
-      value: '4096'
+      value: max_split_size_mb:512