feat: add Motion.Suppressed property to mark tab-gap codes

Adds Suppressed bool to the Motion base class so LinearMove, ArcMove,
and RapidMove can be flagged for skip during rendering and post-processing
when they fall within a tab gap. Clone() updated on all three subclasses
to preserve the flag. Covered by new MotionSuppressedTests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/CNC/ArcMove.cs

@@ -65,7 +65,8 @@ namespace OpenNest.CNC
         {
             return new ArcMove(EndPoint, CenterPoint, Rotation)
             {
-                Layer = Layer
+                Layer = Layer,
+                Suppressed = Suppressed
             };
         }