feat: add scrap zone identification to MultiPlateNester

Adds IsScrapRemnant(), FindScrapZones(), and FindViableRemnants() to
MultiPlateNester. A remnant is scrap only when both dimensions fall
below the minimum remnant size threshold (AND logic, not OR).

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

OpenNest.Engine/MultiPlateNester.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Linq;
+using OpenNest.Engine.Fill;
 using OpenNest.Geometry;
 
 namespace OpenNest
@@ -56,5 +57,40 @@ namespace OpenNest
 
             return PartClass.Small;
         }
+
+        public static bool IsScrapRemnant(Box remnant, double minRemnantSize)
+        {
+            return remnant.Width < minRemnantSize && remnant.Length < minRemnantSize;
+        }
+
+        public static List<Box> FindScrapZones(Plate plate, double minRemnantSize)
+        {
+            var finder = RemnantFinder.FromPlate(plate);
+            var remnants = finder.FindRemnants();
+
+            var scrap = new List<Box>();
+            foreach (var remnant in remnants)
+            {
+                if (IsScrapRemnant(remnant, minRemnantSize))
+                    scrap.Add(remnant);
+            }
+
+            return scrap;
+        }
+
+        public static List<Box> FindViableRemnants(Plate plate, double minRemnantSize)
+        {
+            var finder = RemnantFinder.FromPlate(plate);
+            var remnants = finder.FindRemnants();
+
+            var viable = new List<Box>();
+            foreach (var remnant in remnants)
+            {
+                if (!IsScrapRemnant(remnant, minRemnantSize))
+                    viable.Add(remnant);
+            }
+
+            return viable;
+        }
     }
 }