test(geometry): pin near-zero-sweep arc bounds without a local DXF

DxfImport_ArcBoundingBoxes_Diagnostic read a drawing from one user's
desktop, returned early elsewhere and asserted nothing, so the near-zero
sweep bounding-box fix (4053f1f) had no regression test that could fail.

Replace it with ArcBoundingBoxTests: a forward and a reversed arc with a
sweep below Tolerance.Epsilon must be bounded by its endpoints, and an
ordinary arc crossing 90 degrees must still reach the top of its circle.
With the 4053f1f guard reverted, both near-zero cases fail (the box grows
to the full circle); with it in place all three pass.

OpenNest.Tests/Geometry/ArcBoundingBoxTests.cs

@@ -0,0 +1,54 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Geometry;
+
+/// <summary>
+/// An arc whose sweep is below <c>Tolerance.Epsilon</c> must not be bounded as a full
+/// circle: its box covers only the endpoints. Ordinary arcs still reach the cardinal
+/// extents they cross.
+/// </summary>
+public class ArcBoundingBoxTests
+{
+    private const double Tol = 1e-9;
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void NearZeroSweep_BoundsCoverOnlyTheEndpoints(bool reversed)
+    {
+        var center = new Vector(10, 20);
+        const double radius = 50;
+        const double a = 0.3;
+        const double b = 0.3 + 1e-6; // sweep well below Tolerance.Epsilon (1e-5)
+
+        var arc = reversed
+            ? new Arc(center, radius, b, a, reversed: true)
+            : new Arc(center, radius, a, b);
+
+        var x1 = center.X + radius * System.Math.Cos(a);
+        var y1 = center.Y + radius * System.Math.Sin(a);
+        var x2 = center.X + radius * System.Math.Cos(b);
+        var y2 = center.Y + radius * System.Math.Sin(b);
+        var box = arc.BoundingBox;
+
+        Assert.Equal(System.Math.Min(x1, x2), box.X, Tol);
+        Assert.Equal(System.Math.Min(y1, y2), box.Y, Tol);
+        Assert.Equal(System.Math.Max(x1, x2), box.X + box.Length, Tol);
+        Assert.Equal(System.Math.Max(y1, y2), box.Y + box.Width, Tol);
+    }
+
+    [Fact]
+    public void ArcCrossingQuarterTurn_StillReachesTopOfCircle()
+    {
+        const double radius = 10;
+        const double a = 0.1;
+        var arc = new Arc(new Vector(0, 0), radius, a, System.Math.PI - a);
+
+        var box = arc.BoundingBox;
+
+        Assert.Equal(-radius * System.Math.Cos(a), box.X, Tol);
+        Assert.Equal(radius * System.Math.Sin(a), box.Y, Tol);
+        Assert.Equal(radius * System.Math.Cos(a), box.X + box.Length, Tol);
+        Assert.Equal(radius, box.Y + box.Width, Tol);
+    }
+}

OpenNest.Tests/Geometry/EllipseConverterTests.cs

@@ -3,17 +3,13 @@ using OpenNest.Geometry;
 using OpenNest.IO;
 using OpenNest.Math;
 using Xunit;
-using Xunit.Abstractions;
 
 namespace OpenNest.Tests.Geometry;
 
 public class EllipseConverterTests
 {
-    private readonly ITestOutputHelper _output;
     private const double Tol = 1e-10;
 
-    public EllipseConverterTests(ITestOutputHelper output) => _output = output;
-
     [Fact]
     public void EvaluatePoint_AtZero_ReturnsMajorAxisEnd()
     {
@@ -293,31 +289,6 @@ public class EllipseConverterTests
         }
     }
 
-    [Fact]
-    public void DxfImport_ArcBoundingBoxes_Diagnostic()
-    {
-        var path = @"C:\Users\aisaacs\Desktop\11ga tab.dxf";
-        if (!System.IO.File.Exists(path))
-            return;
-
-        var result = Dxf.Import(path);
-        var all = (System.Collections.Generic.IEnumerable<IBoundable>)result.Entities;
-        var bbox = all.GetBoundingBox();
-        _output.WriteLine(
-            $"Overall: X={bbox.X:F4} Y={bbox.Y:F4} W={bbox.Length:F4} H={bbox.Width:F4}"
-        );
-
-        for (var i = 0; i < result.Entities.Count; i++)
-        {
-            var e = result.Entities[i];
-            var b = e.BoundingBox;
-            var flag = (b.Length > 1 || b.Width > 1) ? " ***" : "";
-            _output.WriteLine(
-                $"{i + 1,3}. {e.GetType().Name,-8} X={b.X:F4} Y={b.Y:F4} W={b.Length:F4} H={b.Width:F4}{flag}"
-            );
-        }
-    }
-
     [Fact]
     public void ToOpenNest_FlippedNormalZ_ProducesCorrectArcs()
     {