getBoundingSphere() {
    return infiniteSphere
  }
Override getBoundingSphere method to handle vertex shader transformation

Notice that for simplicity we just provide an infinite bounding sphere, essentially
bypassing the bounding sphere prefilter and triggering full raycast of all arcs.
This lets us avoid having to track changes to the angle/radius uniform props, and we
can get away with it because the total number of objects in this scene is small enough
that we can just raycast all of them without a bounding sphere prefilter. If that weren't
the case, you'd need to make this sphere more tightly wrapped to the actual arc, and then
in `afterUpdate` you'd need to test whether any of the angle/radius props was changed and
if so send a `this.notifyWorld('object3DBoundsChanged')` message so the raycasting
octree gets updated.