Add disease association annotation to the network.

        :param disease_associations: Dictionary of disease-gene associations.

def _add_disease_associations(self, disease_associations: dict) -> None:
        """Add disease association annotation to the network.

        :param disease_associations: Dictionary of disease-gene associations.
        """
        if disease_associations is not None:
            for target_id, disease_id_list in disease_associations.items():
                if target_id in self.graph.vs["name"]:
                    self.graph.vs.find(name=target_id)["associated_diseases"] = disease_id_list