refactor(engine): precompute hull angles during pair evaluation

Store hull edge angles in BestFitResult at evaluation time so they
don't need to be recomputed during the fill phase. Extract
GetHullEdgeAngles(Polygon) overload from FindHullEdgeAngles.

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

OpenNest.Engine/BestFit/PairEvaluator.cs

@@ -42,6 +42,7 @@ namespace OpenNest.Engine.BestFit
 
             // Find optimal bounding rectangle via rotating calipers
             double bestArea, bestWidth, bestHeight, bestRotation;
+            List<double> hullAngles = null;
 
             if (allPoints.Count >= 3)
             {
@@ -51,6 +52,7 @@ namespace OpenNest.Engine.BestFit
                 bestWidth = result.Width;
                 bestHeight = result.Height;
                 bestRotation = result.Angle;
+                hullAngles = RotationAnalysis.GetHullEdgeAngles(hull);
             }
             else
             {
@@ -59,6 +61,7 @@ namespace OpenNest.Engine.BestFit
                 bestWidth = combinedBox.Width;
                 bestHeight = combinedBox.Length;
                 bestRotation = 0;
+                hullAngles = new List<double> { 0 };
             }
 
             var trueArea = drawing.Area * 2;
@@ -71,6 +74,7 @@ namespace OpenNest.Engine.BestFit
                 BoundingHeight = bestHeight,
                 OptimalRotation = bestRotation,
                 TrueArea = trueArea,
+                HullAngles = hullAngles,
                 Keep = !overlaps,
                 Reason = overlaps ? "Overlap detected" : "Valid"
             };