message: Fix `subscription` for `iced::pure::Application`
diff: @@ -158,6 +158,10 @@ where
  A::update(&mut self.application, message)
  }
  + fn subscription(&self) -> Subscription<Self::Message> {
  + A::subscription(&self.application)
  + }
  +
  fn view(&mut self) -> crate::Element<'_, Self::Message> {
  let content = A::view(&self.application);
  