feat: add LeastCodeSequencer with nearest-neighbor and 2-opt

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

OpenNest.Tests/Sequencing/LeastCodeSequencerTests.cs

@@ -0,0 +1,61 @@
+using System.Collections.Generic;
+using OpenNest.CNC;
+using OpenNest.Engine.Sequencing;
+using OpenNest.Geometry;
+using Xunit;
+
+namespace OpenNest.Tests.Sequencing;
+
+public class LeastCodeSequencerTests
+{
+    private static Part MakePartAt(double x, double y) => TestHelpers.MakePartAt(x, y);
+
+    [Fact]
+    public void NearestNeighbor_FromExitPoint()
+    {
+        var plate = new Plate(60, 120);
+        var farPart = MakePartAt(5, 5);
+        var nearPart = MakePartAt(55, 115);
+        plate.Parts.Add(farPart);
+        plate.Parts.Add(nearPart);
+
+        var sequencer = new LeastCodeSequencer();
+        var result = sequencer.Sequence(plate.Parts.ToList(), plate);
+
+        // nearPart is closer to exit point, should come first
+        Assert.Same(nearPart, result[0].Part);
+        Assert.Same(farPart, result[1].Part);
+    }
+
+    [Fact]
+    public void PreservesAllParts()
+    {
+        var plate = new Plate(60, 120);
+        for (var i = 0; i < 10; i++)
+            plate.Parts.Add(MakePartAt(i * 5, i * 10));
+
+        var sequencer = new LeastCodeSequencer();
+        var result = sequencer.Sequence(plate.Parts.ToList(), plate);
+
+        Assert.Equal(10, result.Count);
+    }
+
+    [Fact]
+    public void TwoOpt_ImprovesSolution()
+    {
+        var plate = new Plate(100, 100);
+        var a = MakePartAt(90, 90);
+        var b = MakePartAt(10, 80);
+        var c = MakePartAt(80, 10);
+        var d = MakePartAt(5, 5);
+        plate.Parts.Add(a);
+        plate.Parts.Add(b);
+        plate.Parts.Add(c);
+        plate.Parts.Add(d);
+
+        var sequencer = new LeastCodeSequencer();
+        var result = sequencer.Sequence(plate.Parts.ToList(), plate);
+
+        Assert.Equal(4, result.Count);
+    }
+}