feat(element/progress): Progress bar implementation as an Element

src/app.zig

@@ -415,6 +415,7 @@ pub fn App(comptime E: type) type {
         pub const Alignment = element.Alignment(Event);
         pub const Button = element.Button(Event, Queue);
         pub const Input = element.Input(Event, Queue);
+        pub const Progress = element.Progress(Event, Queue);
         pub const Scrollable = element.Scrollable(Event);
         pub const Queue = queue.Queue(Event, 256);
     };