docs: def initialize(self, num_of_paths=None, grid=None, seed=None):
          """initialize StackedConsumer"""
          super(StackedConsumer, self).initialize(grid, num_of_paths, seed)
          for c in self.consumers:
              c.initialize(grid, num_of_paths, seed)
          self.state = [c.state for c in self.consumers]