code: def save_state(self, fname):
          
          log.info("Saving state to %s", fname)
          data = {
              'ksize': self.ksize,
              'alpha': self.alpha,
              'id': self.node.id,
              'neighbors': self.bootstrappable_neighbors()
          }
          if not data['neighbors']:
              log.warning("No known neighbors, so not writing to cache.")
              return
          with open(fname, 'wb') as file:
              pickle.dump(data, file)
docs: Save the state of this node (the alpha/ksize/id/immediate neighbors)
          to a cache file with the given fname.