Allow clearing PhysX mesh cache or creating convex meshes from numpy arrays

[ZoneLikeWonderland]

Is your feature request related to a problem? Please describe.
Yes. PhysxCollisionShapeConvexMesh::LoadMultiple uses MeshManager to cache PhysX meshes by filename and never invalidates them (see src/physx/collision_shape.cpp and src/physx/mesh_manager.cpp).

In a long-running process this causes:

• Modified meshes with the same filename cannot be reloaded (old cooked mesh is always reused).
• Memory usage keeps growing as more mesh files are loaded and only drops when the engine/process exits.

Describe the solution you'd like
Either:

• an API to clear or disable the PhysX mesh cache (C++ and/or Python, e.g. engine.clear_mesh_cache()), or
• an API to build convex collision shapes directly from numpy vertices / faces arrays, bypassing filename-based caching.

Describe alternatives you've considered

• Changing the filename each time the mesh changes (works around reload, but makes memory growth even worse).
• Restarting the whole process/engine to release cached meshes.

Both are impractical for long-running services or RL training.

Additional context
Python call site: sapien.physx.PhysxCollisionShapeConvexMesh.load_multiple(...).

[fbxiang]

I have implemented sapien.physx.clear_cache() and supported creating PhysX meshes from vertices. (See commit). The wheel is available in the nightly release and you can try it out. If it works well I will soon publish it to Pypi.

[ZoneLikeWonderland]

It works as expected. Thanks!