fork function
Start a new zone with a new service scope and run func inside it.
The function func must return a Future and the service scope will end
when this future completes.
If an uncaught error occurs and onError is given, it will be called. The
onError parameter can take the same values as Zone.current.fork.
Implementation
Future fork(Future Function() func, {Function? onError}) {
var currentServiceScope = _serviceScope;
currentServiceScope ??= _emptyServiceScope;
return currentServiceScope._fork(func, onError: onError);
}