feat: add AutoSplitCalculator for fit-to-plate and split-by-count

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

OpenNest.Tests/Splitting/SplitLineTests.cs

@@ -1,3 +1,5 @@
+using OpenNest.Geometry;
+
 namespace OpenNest.Tests.Splitting;
 
 public class SplitLineTests
@@ -29,3 +31,57 @@ public class SplitLineTests
         Assert.Equal(2, p.SpikePairCount);
     }
 }
+
+public class AutoSplitCalculatorTests
+{
+    [Fact]
+    public void FitToPlate_SingleAxis_CalculatesCorrectSplits()
+    {
+        var partBounds = new Box(0, 0, 100, 50);
+        var lines = AutoSplitCalculator.FitToPlate(partBounds, 60, 60, 1.0, 0);
+
+        Assert.Single(lines);
+        Assert.Equal(CutOffAxis.Vertical, lines[0].Axis);
+        Assert.Equal(50.0, lines[0].Position, 1);
+    }
+
+    [Fact]
+    public void FitToPlate_BothAxes_GeneratesGrid()
+    {
+        var partBounds = new Box(0, 0, 200, 200);
+        var lines = AutoSplitCalculator.FitToPlate(partBounds, 60, 60, 0, 0);
+
+        var verticals = lines.Where(l => l.Axis == CutOffAxis.Vertical).ToList();
+        var horizontals = lines.Where(l => l.Axis == CutOffAxis.Horizontal).ToList();
+        Assert.Equal(3, verticals.Count);
+        Assert.Equal(3, horizontals.Count);
+    }
+
+    [Fact]
+    public void FitToPlate_AlreadyFits_ReturnsEmpty()
+    {
+        var partBounds = new Box(0, 0, 50, 50);
+        var lines = AutoSplitCalculator.FitToPlate(partBounds, 60, 60, 1.0, 0);
+        Assert.Empty(lines);
+    }
+
+    [Fact]
+    public void SplitByCount_SingleAxis_EvenlySpaced()
+    {
+        var partBounds = new Box(0, 0, 100, 50);
+        var lines = AutoSplitCalculator.SplitByCount(partBounds, horizontalPieces: 1, verticalPieces: 3);
+
+        Assert.Equal(2, lines.Count);
+        Assert.All(lines, l => Assert.Equal(CutOffAxis.Vertical, l.Axis));
+        Assert.Equal(33.333, lines[0].Position, 2);
+        Assert.Equal(66.667, lines[1].Position, 2);
+    }
+
+    [Fact]
+    public void FitToPlate_AccountsForFeatureOverhang()
+    {
+        var partBounds = new Box(0, 0, 100, 50);
+        var lines = AutoSplitCalculator.FitToPlate(partBounds, 60, 60, 1.0, 0.5);
+        Assert.Single(lines);
+    }
+}