Add Gravograph IS post processor

OpenNest.Tests/GravographIS/NestPolylineExtractorTests.cs

@@ -0,0 +1,37 @@
+using OpenNest;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class NestPolylineExtractorTests
+{
+    [Fact]
+    public void ExtractPart_IncrementalProgram_ProducesAbsoluteCoordinates()
+    {
+        // 1x1 square in G91 (incremental) mode — the form OpenNest's UI writes
+        // to .nest files. Without absolute-mode handling the extractor plotted
+        // each EndPoint as if it were absolute, producing a 2x2 diamond.
+        var program = new Program(Mode.Incremental);
+        program.Codes.Add(new RapidMove(new Vector(0, 0)));
+        program.Codes.Add(new LinearMove(1, 0));
+        program.Codes.Add(new LinearMove(0, 1));
+        program.Codes.Add(new LinearMove(-1, 0));
+        program.Codes.Add(new LinearMove(0, -1));
+
+        var drawing = new Drawing("Square 1x1", program);
+        var part = new Part(drawing, new Vector(0.25, 46.75));
+
+        var polylines = new NestPolylineExtractor().ExtractPart(part);
+
+        Assert.Single(polylines);
+        var poly = polylines[0];
+        Assert.Equal(5, poly.Count);
+        Assert.Equal(new Vector(0.25, 46.75), poly[0]);
+        Assert.Equal(new Vector(1.25, 46.75), poly[1]);
+        Assert.Equal(new Vector(1.25, 47.75), poly[2]);
+        Assert.Equal(new Vector(0.25, 47.75), poly[3]);
+        Assert.Equal(new Vector(0.25, 46.75), poly[4]);
+    }
+}