getLazySingletonK<T extends Object>  method 
Retrieves the lazily loaded singleton dependency.
Implementation
@protected
Option<Resolvable<T>> getLazySingletonK<T extends Object>(
  Entity typeEntity, {
  Entity groupEntity = const DefaultEntity(),
  bool traverse = true,
}) {
  final option = getLazyK<T>(
    typeEntity,
    groupEntity: groupEntity,
    traverse: traverse,
  );
  if (option.isNone()) {
    return const None();
  }
  UNSAFE:
  final lazy = option.unwrap().sync().unwrap().unwrap();
  return Some(lazy.singleton);
}