componentDiff method
Compares the component list between entities and returns a list of types of components that "a" has that "b" does not.
E.g.
final compared = a.componentDiff(b);
Implementation
Set<Type> componentDiff(Entity e) {
final ecomps = e.components.value.keys.toSet();
return components.value.keys.toSet().difference(ecomps);
}