fix: correct test helper winding and edge sequencer test data

Test drawings used CCW winding, causing OffsetSide.Left to produce
inward offsets. The BestFit pipeline then positioned pairs so actual
shapes overlapped, failing all 1232 candidates. Changed to CW winding
to match CNC convention where OffsetSide.Left = outward.

Also fixed EdgeStartSequencer test: centerPart at (25,55) was only 4.5
from the top edge (plate Y=60), closer than midPart at (10,10). Moved
to (25,25) for correct ordering.

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

OpenNest.Tests/Sequencing/EdgeStartSequencerTests.cs

@@ -11,7 +11,7 @@ public class EdgeStartSequencerTests
     {
         var plate = new Plate(60, 120);
         var edgePart = MakePartAt(1, 1);
-        var centerPart = MakePartAt(25, 55);
+        var centerPart = MakePartAt(25, 25);
         var midPart = MakePartAt(10, 10);
         plate.Parts.Add(edgePart);
         plate.Parts.Add(centerPart);