fixing the dual function and superkeys triggering issue

[unional]

I am testing it out and I think the fundamental issue is that the triggering flag is shared across keys.
Thus when you type fast, e.g. keydown a -> keydown b -> keyup a -> keydown c -> keyup b -> keydown d -> keyup c -> ..., even keyup a occurs a while back, the triggering time still reach and the function is triggered.

What needs to happen is that each keydown has its own triggering time.
The entries are stored in an array, and when the keyup event occurs that entry needs to be removed.

The logic check what is the oldest triggering time to determine should the function execute.

A further enhancement is to allow each key to have its own triggering threshold. i.e.:

const pressedKeys = [{
  keyCode: 'a',
  triggeredAt: time,
  triggerThreshold: number
}, ...]