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.Engine/RectanglePacking/PackBottomLeft.cs

@@ -1,7 +1,7 @@
-using System.Collections.Generic;
-using System.Linq;
-using OpenNest.Geometry;
+using OpenNest.Geometry;
 using OpenNest.Math;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace OpenNest.RectanglePacking
 {
@@ -71,7 +71,7 @@ namespace OpenNest.RectanglePacking
 
             if (pt.X != double.MaxValue && pt.Y != double.MaxValue)
                 return pt;
-            
+
             return null;
         }