[simplejson] Make JSONEncoder.default return Any, matching json.JSONEncoder

[maroux]

simplejson.JSONEncoder.default is declared -> Never, while the stdlib stub declares json.JSONEncoder.default as -> Any.

default is the hook subclasses override to serialise extra types, so it returns a value; only the base implementation raises. With -> Never, every override that returns something fails the override check. For example, this reports invalid-method-override under ty:

class DateTimeEncoder(simplejson.JSONEncoder):
    def default(self, o: Any) -> str:
        if isinstance(o, datetime):
            return o.isoformat()
        return super().default(o)

This changes the return type to Any, the same as json.JSONEncoder.default, and drops the now-unused Never import.

🤖 Generated with Claude Code

[github-actions]

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