Function cyclotron::lazy_set::depth_first::memoize

pub fn memoize<K, V, A>(
    f: impl FnOnce(K) -> A + Clone
) -> impl FnMut(K) -> BTreeSet<V> where
    K: Copy + Ord + Hash + Debug,
    V: Clone + Ord + Debug,
    A: LazySet<Call<K>, V, Item = V>,