iced-template: factor out Element, explicit Error

the type alias Element is quite useful for defining subfunctions for view
and it also helps to not pull unnecessary things into scope

src/app/mod.rs

@@ -1,4 +1,6 @@
-use iced::{Color, Element, Renderer, Task, Theme, application, theme, widget};
+use iced::{Color, Task, application, theme, widget};
+
+type Element<'a> = iced::Element<'a, Message, iced::Theme, iced::Renderer>;
 
 enum Message {}
 
@@ -11,12 +13,12 @@ impl State {
     fn update(&mut self, message: Message) -> Task<Message> {
         Task::none()
     }
-    fn view(&self) -> Element<'_, Message, Theme, Renderer> {
+    fn view(&self) -> Element<'_> {
         widget::text("hiiiiiii").into()
     }
 }
 
-pub fn run() -> Result<(), impl std::error::Error> {
+pub fn run() -> Result<(), iced::Error> {
     application(State::new, State::update, State::view)
         .theme(theme::Theme::custom(
             "high-contrast-dark",