Disallows duplcates on-handlers on particular store.
const increment = createEvent();
// 👍 all explicitly
const $goodCounter = createStore(0).on(increment, (counter) => counter + 1);
// 👎 so, which handler should we choose?
// it's better to remove one of them
const $badCounter = createStore(0)
.on(increment, (counter) => counter + 1)
.on(increment, (counter) => counter + 2);