derive `Default` for `Stateful`

Please complete the following tasks

[X] I have searched the discussions
[X] I have searched the open and rejected issues

winnow version

0.6.8

Describe your use case

I want to utilize the subparser pattern, to minimize the scope of the parser state.

Currently, my solution is like this:

fn with_state<S, State, O, ParseNext>(mut parse_next: ParseNext) -> impl Parser<S, O, ContextError>
where
    S: TokenStream,
    State: Default,
    ParseNext: Parser<Stateful<S, State>, O, ContextError>,
{
    move |input: &mut S| -> PResult<O> {
        let state = State::default();
        let input2 = std::mem::take(input);
        let mut stateful = Stateful {
            input: input2,
            state,
        };
        let output = parse_next.parse_next(&mut stateful);
        *input = stateful.input;
        output
    }
}

This works well, unless I want to use Stateful<Stateful<S, State1>, State2>, which doesn't implement Default even if both S, State1 and State2 implemented Default.

Describe the solution you'd like

Derive Default for Stateful.

It's harmless for any other use case. Only when both input and state implemented Default, Stateful<I, S> will implemented Default.

Alternatives, if applicable

No response

Additional Context