perf: optimize fill hot path — bbox pre-check and geometry inner loop

- Add bounding box rejection in HasOverlaps to skip expensive
  Part.Intersects (CNC→geometry conversion) for non-adjacent parts.
  Eliminates ~35% CPU in IsBetterValidFill for grid layouts.
- Optimize RayEdgeDistance: access Line fields directly instead of
  property getters (avoids Vector struct copies), inline IsEqualTo
  with direct range comparison (avoids Math.Abs), and precompute
  deltas for reuse in interpolation.
- Cache line endpoints in DirectionalDistance outer loop to avoid
  repeated struct copies in the inner loop.
- Add fill timer to ActionClone.Fill, displayed in PlateView status
  bar as "Fill: N parts in M ms".

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

OpenNest/Actions/ActionClone.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.Linq;
 using System.Windows.Forms;
 using OpenNest.Controls;
@@ -170,6 +171,8 @@ namespace OpenNest.Actions
 
         private void Fill()
         {
+            var sw = Stopwatch.StartNew();
+
             var plate = plateView.Plate;
             var engine = new NestEngine(plate);
             var groupParts = parts.Select(p => p.BasePart).ToList();
@@ -179,6 +182,8 @@ namespace OpenNest.Actions
             if (plate.Parts.Count == 0)
             {
                 engine.Fill(groupParts);
+                sw.Stop();
+                plateView.Status = $"Fill: {plate.Parts.Count} parts in {sw.ElapsedMilliseconds} ms";
                 return;
             }
 
@@ -197,7 +202,10 @@ namespace OpenNest.Actions
             if (bestArea == Box.Empty)
                 return;
 
+            var before = plate.Parts.Count;
             engine.Fill(groupParts, bestArea);
+            sw.Stop();
+            plateView.Status = $"Fill: {plate.Parts.Count - before} parts in {sw.ElapsedMilliseconds} ms";
         }
     }
 }

OpenNest/Controls/PlateView.cs

@@ -139,7 +139,7 @@ namespace OpenNest.Controls
         public string Status
         {
             get { return status; }
-            protected set
+            set
             {
                 status = value;