fix(core): stop Part.Clone from double-counting baked drawing rotation

Part.Clone() rebuilt the clone from BaseDrawing and then re-applied the
part's absolute Rotation on top of it. Since BaseDrawing.Program.Rotation
is itself absolute (baked in), this double-counted it whenever the base
drawing already carried a nonzero rotation, silently corrupting the
clone's orientation while its Location stayed unchanged.

This only manifests for drawings needing canonical-frame axis correction
(nonzero Source.Angle), since DefaultPlateFiller wraps every drawing in a
rotated canonical copy before running any fill strategy. FillHelpers.
BuildRotatedPattern clones parts before tiling, so any strategy that
tiles interlocking pairs (Pairs, Strip/Remnant, Column/Row) could produce
overlapping placements for such drawings.

Fix: clone the already-composed Program directly instead of re-deriving
rotation from BaseDrawing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

OpenNest.Core/Part.cs

@@ -294,9 +294,18 @@ namespace OpenNest
         /// <returns></returns>
         public object Clone()
         {
-            var part = new Part(BaseDrawing);
-            part.Rotate(Rotation);
-            part.Location = Location;
+            // Clone the current Program directly rather than rebuilding from BaseDrawing and
+            // re-rotating by the absolute Rotation: when BaseDrawing.Program.Rotation is nonzero
+            // (e.g. a canonical-frame copy used internally during fill), `new Part(BaseDrawing)`
+            // already carries that baked rotation, so re-applying the full absolute Rotation on
+            // top of it double-counts the baseline and corrupts the clone's orientation.
+            var part = new Part(
+                BaseDrawing,
+                (Program)Program.Clone(),
+                Location,
+                new Box(BoundingBox.X, BoundingBox.Y, BoundingBox.Length, BoundingBox.Width)
+            );
+            part.ownsProgram = true;
 
             return part;
         }