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/HorizontalRemnantEngine.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using OpenNest.Engine;
-using OpenNest.Engine.BestFit;
 using OpenNest.Engine.Fill;
 using OpenNest.Geometry;
 using OpenNest.Math;
@@ -27,20 +26,6 @@ namespace OpenNest
 
         public override ShrinkAxis TrimAxis => ShrinkAxis.Length;
 
-        protected override BestFitResult SelectBestFitPair(List<BestFitResult> results)
-        {
-            BestFitResult best = null;
-
-            foreach (var r in results)
-            {
-                if (!r.Keep) continue;
-                if (best == null || r.BoundingHeight < best.BoundingHeight)
-                    best = r;
-            }
-
-            return best;
-        }
-
         public override List<double> BuildAngles(NestItem item, ClassificationResult classification, Box workArea)
         {
             var baseAngles = new List<double> { classification.PrimaryAngle, classification.PrimaryAngle + Angle.HalfPI };