fix(opus55): cut clearance margin to 0.003 and drop etch marks from geometry

The 0.022 margin assumed validators flatten arcs at 0.01; NestValidator
uses 0.001, so a pair can read at most 0.002 closer than true. 0.003
covers that plus the 1e-4 Clipper grid, returning ~0.019 per gap. Arc,
disc, obround and zero-spacing tests still pass.

Part geometry filtered only rapids, so scribe/etch moves counted as
material - the bug OpenNest fixed in 1b5e1b1. Use SpecialLayers.IsMaterial.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Engine.Opus55/tests/Opus55NestingEngineTests.cs

@@ -191,6 +191,24 @@ public class Opus55NestingEngineTests
         Assert.Equal(Describe(first), Describe(second));
     }
 
+    [Fact]
+    public void EtchMarksAreLeftOutOfNestingGeometry()
+    {
+        // A bend tick starts on material and ends 1.0 into a side notch, outside the part but
+        // inside its bounding box (the PEP case that crashed nesting before 1b5e1b1). As
+        // material it is open geometry leaving the part; as a mark it must be ignored.
+        var etched = Polyline((0, 0), (10, 0), (10, 4), (8, 4), (8, 6), (10, 6), (10, 10), (0, 10));
+        etched.Codes.Add(new RapidMove(7.5, 5));
+        etched.Codes.Add(new LinearMove(9, 5) { Layer = LayerType.Scribe });
+        var job = Job(new[] { Part("part", etched, 2, RotationPolicy.Fixed(0)) }, new[] { Stock("sheet", 10.4, 20.6, spacing: 0.2) });
+
+        var result = new Opus55NestingEngine().Solve(job);
+
+        AssertValid(job, result);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(2, Assert.Single(result.Plates).Placements.Count);
+    }
+
     [Fact]
     public void HasPublicParameterlessConstructorForPluginDiscovery()
     {