Fix some types to peewee

[s-yh-china]

Among the methods that originally returned None type, there are some of methods annotated by @Node.copy
according to the code review, it can be inferred that these methods actually return type Self

    @staticmethod
    def copy(method):
        def inner(self, *args, **kwargs):
            clone = self.clone()
            method(clone, *args, **kwargs)
            return clone
        return inner

so I fixed these incorrect return type

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉