docs: def cache(self):
          """Cache the Zotero data."""
          with open(self.cache_path, "wb") as f:
              cache = {self.CACHE_REFERENCE_LIST: self._references,
                       self.CACHE_REFERENCE_TYPES: self.reference_types,
                       self.CACHE_REFERENCE_TEMPLATES: self.reference_templates}
              pickle.dump(cache, f)