docs: def to_meta_df(trained_regressor,
                 target_gene_name):
      """
      :param trained_regressor: the trained model from which to extract the meta information.
      :param target_gene_name: the name of the target gene.
      :return: a Pandas DataFrame containing side information about the regression.
      """
      n_estimators = len(trained_regressor.estimators_)
  
      return pd.DataFrame({'target': [target_gene_name], 'n_estimators': [n_estimators]})