feat: serialize plate optimizer settings in nest files

Add PlateOptions and SalvageRate properties to the Nest class and
round-trip them through NestWriter/NestReader via a new PlateOptionDto.

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

OpenNest.Core/Nest.cs

@@ -1,6 +1,7 @@
 using OpenNest.Collections;
 using OpenNest.Geometry;
 using System;
+using System.Collections.Generic;
 
 namespace OpenNest
 {
@@ -51,6 +52,10 @@ namespace OpenNest
 
         public PlateSettings PlateDefaults { get; set; }
 
+        public List<PlateOption> PlateOptions { get; set; } = new();
+
+        public double SalvageRate { get; set; } = 0.5;
+
         public Plate CreatePlate()
         {
             var plate = PlateDefaults.CreateNew();

OpenNest.IO/NestFormat.cs

@@ -29,6 +29,8 @@ namespace OpenNest.IO
             public PlateDefaultsDto PlateDefaults { get; init; } = new();
             public List<DrawingDto> Drawings { get; init; } = new();
             public List<PlateDto> Plates { get; init; } = new();
+            public List<PlateOptionDto> PlateOptions { get; init; } = new();
+            public double SalvageRate { get; init; } = 0.5;
         }
 
         public record PlateDefaultsDto
@@ -153,6 +155,13 @@ namespace OpenNest.IO
             public string NoteText { get; init; } = "";
         }
 
+        public record PlateOptionDto
+        {
+            public double Width { get; init; }
+            public double Length { get; init; }
+            public double Cost { get; init; }
+        }
+
         public record BestFitSetDto
         {
             public double PlateWidth { get; init; }

OpenNest.IO/NestReader.cs

@@ -192,6 +192,18 @@ namespace OpenNest.IO
             nest.PlateDefaults.PartSpacing = pd.PartSpacing;
             nest.PlateDefaults.EdgeSpacing = new Spacing(pd.EdgeSpacing.Left, pd.EdgeSpacing.Bottom, pd.EdgeSpacing.Right, pd.EdgeSpacing.Top);
 
+            // Plate optimizer settings
+            nest.SalvageRate = dto.SalvageRate;
+            if (dto.PlateOptions != null)
+            {
+                nest.PlateOptions = dto.PlateOptions.Select(o => new PlateOption
+                {
+                    Width = o.Width,
+                    Length = o.Length,
+                    Cost = o.Cost,
+                }).ToList();
+            }
+
             // Drawings
             foreach (var d in drawingMap.OrderBy(k => k.Key))
                 nest.Drawings.Add(d.Value);

OpenNest.IO/NestWriter.cs

@@ -88,7 +88,14 @@ namespace OpenNest.IO
                 },
                 PlateDefaults = BuildPlateDefaultsDto(),
                 Drawings = BuildDrawingDtos(),
-                Plates = BuildPlateDtos()
+                Plates = BuildPlateDtos(),
+                PlateOptions = nest.PlateOptions?.Select(o => new PlateOptionDto
+                {
+                    Width = o.Width,
+                    Length = o.Length,
+                    Cost = o.Cost,
+                }).ToList() ?? new(),
+                SalvageRate = nest.SalvageRate,
             };
         }