feat: add Part.HasManualLeadIns flag

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

OpenNest.Core/Part.cs

@@ -51,6 +51,8 @@ namespace OpenNest
 
         public Program Program { get; private set; }
 
+        public bool HasManualLeadIns { get; set; }
+
         /// <summary>
         /// Gets the rotation of the part in radians.
         /// </summary>

OpenNest.Engine.Tests/PartFlagTests.cs

@@ -0,0 +1,32 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using Xunit;
+
+namespace OpenNest.Engine.Tests;
+
+public class PartFlagTests
+{
+    [Fact]
+    public void HasManualLeadIns_DefaultsFalse()
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        var drawing = new Drawing("test", pgm);
+        var part = new Part(drawing);
+
+        Assert.False(part.HasManualLeadIns);
+    }
+
+    [Fact]
+    public void HasManualLeadIns_CanBeSet()
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        var drawing = new Drawing("test", pgm);
+        var part = new Part(drawing);
+
+        part.HasManualLeadIns = true;
+
+        Assert.True(part.HasManualLeadIns);
+    }
+}