newCallbackWithoutHandle function
Creates a new callback without a handle.
Returns a Callback instance with the specified function type.
Implementation
Callback<CbFuncWithoutHandle> newCallbackWithoutHandle() {
  final completer = Completer<AskarCallbackResult>();
  late final NativeCallable<CbFuncWithoutHandle> nativeCallable;
  void callback(int callbackId, int errorCode) {
    completer.complete(AskarCallbackResult(ErrorCode.fromInt(errorCode), true, null));
    nativeCallable.close();
  }
  nativeCallable = NativeCallable<CbFuncWithoutHandle>.listener(callback);
  return Callback<CbFuncWithoutHandle>(nativeCallable, completer, nextCallbackId());
}