Turn off vulkan because it's slow on windows

src/app.rs

@@ -44,7 +44,7 @@ struct AppWindow {
 impl AppWindow {
     fn setup_gpu(event_loop: &ActiveEventLoop, client: &EmulatorClient) -> Self {
         let instance = wgpu::Instance::new(wgpu::InstanceDescriptor {
-            backends: wgpu::Backends::PRIMARY,
+            backends: wgpu::Backends::PRIMARY.difference(wgpu::Backends::VULKAN),
             ..Default::default()
         });