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

[srittau]

I don't have experience with peewee, but the changes seem correct to me. But mypy seems to have a problem with the same method returning Self in two different base classes:

from typing import Self

class Base1:
    def foo(self) -> Self:
        return self
    
class Base2:
    def foo(self) -> Self:
        return self
    
class Sub(Base1, Base2):  # error: Definition of "foo" in base class "Base1" is incompatible with definition in base class "Base2"  [misc]
    pass

(python/mypy#14640)

I'm not sure why that is, but for the moment the best solution is to mark those lines with # type: ignore[misc].

[s-yh-china]

thank you for your reminder. i will first add # type: ignore [misc] to pass the check

[github-actions]

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