docs: def proc_state(self, state_data, state_id):
          """Processes a state into an `Assembly`.
  
          Parameters
          ----------
          state_data : dict
              Contains information about the state, including all
              the per line structural data.
          state_id : str
              ID given to `Assembly` that represents the state.
          """
          assembly = Assembly(assembly_id=state_id)
          for k, chain in sorted(state_data.items()):
              assembly._molecules.append(self.proc_chain(chain, assembly))
          return assembly