docs: def list_depth(list_, func=max, _depth=0):
      """
      Returns the deepest level of nesting within a list of lists
  
      Args:
         list_  : a nested listlike object
         func   : depth aggregation strategy (defaults to max)
         _depth : internal var
  
      Example:
          >>> # ENABLE_DOCTEST
          >>> from utool.util_list import *  # NOQA
          >>> list_ = [[[[[1]]], [3]], [[1], [3]], [[1], [3]]]
          >>> result = (list_depth(list_, _depth=0))
          >>> print(result)
  
      """
      depth_list = [list_depth(item, func=func, _depth=_depth + 1)
                    for item in  list_ if util_type.is_listlike(item)]
      if len(depth_list) > 0:
          return func(depth_list)
      else:
          return _depth