unregister method
Unregisters one contribution by pluginId + slot.
Implementation
bool unregister({required String pluginId, required TSlot slot}) {
final index = _registrations.indexWhere(
(registration) =>
registration.pluginId == pluginId && registration.slot == slot,
);
if (index == -1) {
return false;
}
_registrations.removeAt(index);
_notifyListeners();
return true;
}