WIP add Effect for a KV cache

[lukewilliamboswell]

The next step I think is to implement the store using something like

# This is a temporary implementation until effect interpreters are implemented 
fn get_global_hashmap() -> MutexGuard<'static, HashMap<String, u16>> {
    static map: OnceLock<Mutex<HashMap<String, u16>>> = OnceLock::new();
    map.get_or_init(|| Mutex::new(HashMap::new()))
        .lock()
        .expect("Let's hope the lock isn't poisoned")
}

[lukewilliamboswell]

Closing this as no longer planned.