perf: optimize best fit computation and plate optimizer

- Try all valid best fit pairs instead of only the first when qty=2,
  picking the best via IsBetterFill comparer (fixes suboptimal plate
  selection during auto-nesting)
- Pre-compute best fits across all plate sizes once via
  BestFitCache.ComputeForSizes instead of per-size GPU evaluation
- Early exit plate optimizer when all items fit (salvage < 100%)
- Trim slide offset sweep range to 50% overlap to reduce candidates
- Use actual geometry (ray-arc/ray-circle intersection) instead of
  tessellated polygons for slide distance computation — eliminates
  the massive line count from circle/arc tessellation
- Add RayArcDistance and RayCircleDistance to SpatialQuery
- Add PartGeometry.GetOffsetPerimeterEntities for non-tessellated
  perimeter extraction
- Disable GPU slide computer (slower than CPU currently)
- Remove dead SelectBestFitPair virtual method and overrides

Reduces best fit computation from 7+ minutes to ~4 seconds for a
73x25" part with 30+ holes on a 48x96 plate.

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

OpenNest.Engine/DefaultNestEngine.cs

@@ -139,24 +139,42 @@ namespace OpenNest
             var bestFits = BestFitCache.GetOrCompute(
                 drawing, Plate.Size.Length, Plate.Size.Width, Plate.PartSpacing);
 
-            var best = SelectBestFitPair(bestFits);
-            if (best == null)
-                return null;
+            List<Part> bestPlacement = null;
 
-            // BuildParts produces landscape orientation (Width >= Height).
-            // Try both landscape and portrait (90° rotated) and let the
-            // engine's comparer pick the better orientation.
-            var landscape = best.BuildParts(drawing);
-            var portrait = RotatePair90(landscape);
+            foreach (var fit in bestFits)
+            {
+                if (!fit.Keep)
+                    continue;
 
-            var lFits = TryOffsetToWorkArea(landscape, workArea);
-            var pFits = TryOffsetToWorkArea(portrait, workArea);
+                // Skip pairs that can't possibly fit the work area in either orientation.
+                if (fit.ShortestSide > System.Math.Min(workArea.Width, workArea.Length) + Tolerance.Epsilon)
+                    continue;
+                if (fit.LongestSide > System.Math.Max(workArea.Width, workArea.Length) + Tolerance.Epsilon)
+                    continue;
 
-            if (!lFits && !pFits)
-                return null;
-            if (lFits && pFits)
-                return IsBetterFill(portrait, landscape, workArea) ? portrait : landscape;
-            return lFits ? landscape : portrait;
+                var landscape = fit.BuildParts(drawing);
+                var portrait = RotatePair90(landscape);
+
+                var lFits = TryOffsetToWorkArea(landscape, workArea);
+                var pFits = TryOffsetToWorkArea(portrait, workArea);
+
+                // Pick the better orientation for this pair.
+                List<Part> candidate = null;
+                if (lFits && pFits)
+                    candidate = IsBetterFill(portrait, landscape, workArea) ? portrait : landscape;
+                else if (lFits)
+                    candidate = landscape;
+                else if (pFits)
+                    candidate = portrait;
+
+                if (candidate == null)
+                    continue;
+
+                if (bestPlacement == null || IsBetterFill(candidate, bestPlacement, workArea))
+                    bestPlacement = candidate;
+            }
+
+            return bestPlacement;
         }
 
         private static List<Part> RotatePair90(List<Part> parts)