[BUG] 无法打开生成的30p30n-hybrid.vtk

## Bug 描述
按照示例代码python PyMeshGen.py --case "./config/30p30n.json"，生成示例网格‘30p30n-hybrid.vtk’，然后用软件打开出错，

<img width="903" height="225" alt="Image" src="https://github.com/user-attachments/assets/a9ad524f-dcbe-4192-9afe-fb00a5db0ef3" />

