add more optimization for pure node operations

[safareli]

in _map we have

if (aff.tag === Aff.Pure.tag) {
  return Aff.Pure(f(aff._1));
}

same could be done in apply:

if (effF.tag === Aff.Pure.tag) {
  if (eff.tag === Aff.Pure.tag) {
    return new Aff.Pure(effF._0(eff._0));
  }
  return new Aff.Map(effF._0, eff);
}

and in bind:

if (eff.tag == PURE) {
  return f(eff._0);
}