Static Plane collider

Convenience composition: one Plane prim with a collider and no rigid body, the usual ground plane (a PxRigidStatic with a PxPlaneGeometry). Owns no columns; everything comes from the listed components.

• Type: Plane

• Required APIs: PhysicsCollisionAPI

• Optional APIs: PhysxCollisionAPI

• Helper: create_static_plane_colliders()