Add persistent nested-copy symbol settings and transactional imports

src/app/update/file.rs

@@ -404,6 +404,7 @@ impl OpenCADStudio {
             double_click_block_refedit: self.double_click_block_refedit,
             double_click_block_attedit: self.double_click_block_attedit,
             grip_object_limit: self.grip_object_limit,
+            ncopy_bind: self.ncopy_bind,
             cursor_type: self.cursor_type,
             crosshair_color: self.crosshair_color,
             lineweight_display_scale: self.lineweight_display_scale,
@@ -467,6 +468,7 @@ impl OpenCADStudio {
         self.double_click_block_refedit = s.double_click_block_refedit;
         self.double_click_block_attedit = s.double_click_block_attedit;
         self.grip_object_limit = s.grip_object_limit.clamp(0, 32767);
+        self.ncopy_bind = s.ncopy_bind;
         self.cursor_type = s.cursor_type;
         self.crosshair_color = s.crosshair_color;
         self.crosshair_color_input = s