fix: sync to real-machine verified version — ALL TESTS PASSED

真机验证通过的精确版本:
- CUB_NS_QUALIFIER (不是 cub::)
- thread_local inside_cub reentrant guard
- 去掉 -D_CCCL_COMPILER_GCC=1
- total_mem → total_memory

BI-V100 32GB × Iluvatar, CoreX clang++ 编译 51864 bytes .so
expandable_segments:True 被 strip, CUB allocator 接管, 缓存复用确认

qwen3_6_scripts/cccl_preload/verify_preload.py

@@ -28,7 +28,7 @@ if not torch.cuda.is_available():
 
 device = torch.device("cuda:0")
 print(f"Device: {torch.cuda.get_device_name(0)}")
-print(f"Memory: {torch.cuda.get_device_properties(0).total_mem / 1024**3:.1f} GB")
+print(f"Memory: {torch.cuda.get_device_properties(0).total_memory / 1024**3:.1f} GB")
 print()
 
 # Test 1: Basic allocation