Redraw continuously instead of busy-waiting at 100% CPU

Previously, Pteropus would only redraw when the window was resized, but
it would continuously poll for events, keeping a CPU core at 100% even
when not doing anything.

It now automatically queues a new RedrawRequested event after each draw
finishes. The view() call will also limit the frame rate to the video
refresh rate and block when there are more than three frames queued up,
so we're not busywaiting any more.

src/app/mod.rs

@@ -106,6 +106,7 @@ impl MvuApp<Model> for App {
         let mut config = surface
             .get_default_config(&adapter, size.width, size.height)
             .unwrap();
+        config.present_mode = wgpu::PresentMode::AutoVsync;
         config.view_formats.push(config.format);
         surface.configure(&device, &config);
 

src/native/mod.rs

@@ -45,6 +45,10 @@ where
         block_on(self.app.init(&instance, surface, Size2i { width, height }));
     }
 
+
+    // TODO: The idea with these `block_on()` calls is that eventually I'll
+    // write an async executor that runs on top of the winit even loop and then
+    // this stuff can be properly async.
     fn window_event(&mut self, event_loop: &ActiveEventLoop, _id: WindowId, event: WindowEvent) {
         match event {
             WindowEvent::Resized(new_size) => block_on(self.app.resize(Size2i {
@@ -55,7 +59,10 @@ where
                 println!("The close button was pressed; stopping");
                 event_loop.exit();
             }
-            WindowEvent::RedrawRequested => block_on(self.app.view(self.model.clone())).unwrap(),
+            WindowEvent::RedrawRequested => {
+                block_on(self.app.view(self.model.clone())).unwrap();
+                self.window.as_ref().unwrap().request_redraw();
+            },
             WindowEvent::DroppedFile(file_path) => {
                 self.model = block_on(
                     self.app