Memory leak in `recursive` when using `define` function

[mattnenterprise]

The recursive implementation leaks memory if it references itself and the parser definition is defined using the define function. See the following example that creates millions of parsers, but the memory is never released.

use chumsky::prelude::*;

#[derive(Debug, PartialEq)]
enum Chain {
    End,
    Link(char, Box<Chain>),
}

fn parser() -> impl Parser<char, Chain, Error = Simple<char>> {
    let mut chain = Recursive::<_, _, Simple<char>>::declare();

    chain.define(just('+')
        .then(chain.clone())
        .map(|(c, chain)| Chain::Link(c, Box::new(chain)))
        .or_not()
        .map(|chain| chain.unwrap_or(Chain::End)));

    chain
}

fn main() {
    for _n in 1..100_000_000 {
        parser();
    }
}

I originally found this issue in the jaq filter parser here.