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/Motion.cs

@@ -12,6 +12,8 @@ namespace OpenNest.CNC
 
         public int Feedrate { get; set; }
 
+        public bool Suppressed { get; set; }
+
         protected Motion()
         {
             Feedrate = CNC.Feedrate.UseDefault;