MpMcQueue breaks a basic invariant under self-requeue test

[nodakai]

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=0a9dde3dac37be94314c5719726060c7

        #[test]
        fn test_() {
            const N: usize = 4;

            let q0 = Q::<u8, N>::new();
            for i in 0..N {
                q0.enqueue(i as u8).expect("new enqueue");
            }
            eprintln!("start!");

            std::thread::scope(|sc| {
                for i in 0..2 {
                    sc.spawn(|| {
                        for k in 0..1000_000 {
                            if let Some(v) = q0.dequeue() {
                                q0.enqueue(v).unwrap_or_else(|v| panic!("{}: q0 -> q0: {}, {:?}", k, v, to_vec(&q0)));
                            }
                        }
                    });
                }
            });
        }

        fn to_vec<T, const N: usize>(q: &Q<T, N>) -> Vec<T> {  // inaccurate
            let mut ret = vec![];
            while let Some(v) = q.dequeue() {
                ret.push(v);
            }
            ret
        }

Confirmed an implementation based on a mutex, and another based on ring-channel didn't panic