chore: sort using directives

Auto-formatter reordering of using statements across the solution.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Plate.cs

@@ -1,9 +1,9 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using OpenNest.Collections;
+using OpenNest.Collections;
 using OpenNest.Geometry;
 using OpenNest.Math;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace OpenNest
 {