mod: change interface for rendering of Layouts and Widgets to use a non-const pointer to the renderer instead

src/widget/Spacer.zig

@@ -31,7 +31,7 @@ pub fn Widget(comptime Event: type, comptime Renderer: type) type {
             return null;
         }
 
-        pub fn render(this: *@This(), renderer: Renderer) !void {
+        pub fn render(this: *@This(), renderer: *Renderer) !void {
             try renderer.clear(this.size);
         }
     };