refactor: remove StripNestResult.RemnantBox

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest.Engine/StripNestEngine.cs

@@ -298,7 +298,6 @@ namespace OpenNest
             result.StripBox = direction == StripDirection.Bottom
                 ? new Box(workArea.X, workArea.Y, workArea.Width, bestDim)
                 : new Box(workArea.X, workArea.Y, bestDim, workArea.Length);
-            result.RemnantBox = remnantBox;
             result.Score = FillScore.Compute(allParts, workArea);
 
             return result;

OpenNest.Engine/StripNestResult.cs

@@ -7,7 +7,6 @@ namespace OpenNest
     {
         public List<Part> Parts { get; set; } = new();
         public Box StripBox { get; set; }
-        public Box RemnantBox { get; set; }
         public FillScore Score { get; set; }
         public StripDirection Direction { get; set; }
     }