perf(fill): short-circuit default comparisons by count

OpenNest.Engine/Fill/DefaultFillComparer.cs

@@ -17,6 +17,9 @@ namespace OpenNest.Engine.Fill
             if (current == null || current.Count == 0)
                 return true;
 
+            if (candidate.Count != current.Count)
+                return candidate.Count > current.Count;
+
             return FillScore.Compute(candidate, workArea) > FillScore.Compute(current, workArea);
         }
     }

OpenNest.Engine/Fill/FillScore.cs

@@ -26,6 +26,8 @@ namespace OpenNest.Engine.Fill
             if (parts == null || parts.Count == 0)
                 return default;
 
+            PerfCounters.CountFillScoreComputation();
+
             var totalPartArea = 0.0;
             var minX = double.MaxValue;
             var minY = double.MaxValue;