Add stage methods at runtime.

        Stage methods all follow the same pattern.

        :param name: Stage name.

def _add_stage(self, name):
        """ Add stage methods at runtime.

        Stage methods all follow the same pattern.

        :param name: Stage name.
        """
        def stage_func(self, *args, **kwargs):
            """ Stage function.

            :param args: Positional arguments.
            :param kwargs: Keyword arguments.
            :return: Pipeline (for method chaining).
            """
            self._pipe.append(Stage(name, args, kwargs))
            return self

        setattr(Pipeline, name, stage_func)