perf(core): optimize geometry with edge pruning and vertex dedup

Vector implements IEquatable<Vector> with proper GetHashCode for HashSet usage.
Polygon.FindCrossing uses bounding-box pruning to skip non-overlapping edge pairs.
Helper.DirectionalDistance deduplicates vertices via HashSet, sorts edges for
early-exit pruning, and adds a new array-based overload that avoids allocations.
PartBoundary sorts directional edges and exposes GetEdges for zero-alloc access.

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

OpenNest.Engine/PartBoundary.cs

@@ -93,10 +93,10 @@ namespace OpenNest
                 }
             }
 
-            leftEdges = left.ToArray();
-            rightEdges = right.ToArray();
-            upEdges = up.ToArray();
-            downEdges = down.ToArray();
+            leftEdges = left.OrderBy(e => System.Math.Min(e.Item1.Y, e.Item2.Y)).ToArray();
+            rightEdges = right.OrderBy(e => System.Math.Min(e.Item1.Y, e.Item2.Y)).ToArray();
+            upEdges = up.OrderBy(e => System.Math.Min(e.Item1.X, e.Item2.X)).ToArray();
+            downEdges = down.OrderBy(e => System.Math.Min(e.Item1.X, e.Item2.X)).ToArray();
         }
 
         /// <summary>
@@ -152,5 +152,14 @@ namespace OpenNest
                 default:                  return _leftEdges;
             }
         }
+
+        /// <summary>
+        /// Returns the pre-computed edge arrays for the given direction.
+        /// These are in part-local coordinates (no translation applied).
+        /// </summary>
+        public (Vector start, Vector end)[] GetEdges(PushDirection direction)
+        {
+            return GetDirectionalEdges(direction);
+        }
     }
 }