code: def register_custom_groupby_agg_func(method_name: str):
      def wrap(func_type: Type[DataFrameCustomGroupByAggMixin]):
          custom_agg_functions[method_name] = func_type
          return func_type
  
      return wrap
  
file_path: mars/mars/dataframe/groupby/custom_aggregation.py
imports: from abc import ABC, abstractmethod
  from typing import Dict, Type, Union
  import pandas
label_desc: Use image node_id 1 for calling a global function with example usage: register_custom_groupby_agg_func(method_name) and returns: wrap, func_type