chore: Remove unused using statements

Cleanup of unnecessary imports across the codebase.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CutList.Core/Nesting/BestFitEngine.cs

@@ -1,7 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Data;
-using System.Linq;
+using System.Data;
 
 namespace CutList.Core.Nesting
 {
@@ -70,7 +67,7 @@ namespace CutList.Core.Nesting
                 if (best_bin != null)
                     best_bin.AddItem(item);
 
-                
+
             }
 
             return bins