graphics: address performance regression with Image Resize (#504)

## Link to GitHub Issue, if one exists
Regressed by #401 

## Description of change
Two things from testing SDVX Live2D -

1. ColorFill is almost always too expensive and will lead to drops
1. Scale factor of 0.5 causes GPU to sync and causes drops

(ARGB/XRGB doesn't matter, linear filtering doesn't matter)

1 is fixed by removing ColorFill calls on every frame - instead only do
this once when the user changes the duplicate option (on the next frame)

2 is fixed by updating the UI (limit the slider) though people can
ctrl+click to override these slider limits.

The warning label will be kept with slightly reworded text.

## Testing
tested in sdvx eg final (sudden death) - on my RTX 4070, my FPS is rock
solid 120 fps even with image resize on now.

src/spice2x/cfg/screen_resize.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <atomic>
 #include <memory>
 #include <string>
 #include <optional>
@@ -51,6 +52,9 @@ namespace cfg {
         bool enable_linear_filter = true;
         fullscreen_setting scene_settings[4];
 
+        // state
+        std::atomic<bool> need_surface_clean = false;
+
         // windowed mode sizing
         // Windows terminology:
         //     window = rectangle including the frame