code: def _get_reference(self):
          
          super()._get_reference()
          self.cube_body_id = self.sim.model.body_name2id("cube")
          self.l_finger_geom_ids = [
              self.sim.model.geom_name2id(x) for x in self.gripper.left_finger_geoms
          ]
          self.r_finger_geom_ids = [
              self.sim.model.geom_name2id(x) for x in self.gripper.right_finger_geoms
          ]
          self.cube_geom_id = self.sim.model.geom_name2id("cube")
docs: Sets up references to important components. A reference is typically an
          index or a list of indices that point to the corresponding elements
          in a flatten array, which is how MuJoCo stores physical simulation data.