style: apply CSharpier formatting to all C# sources

Repo-wide sweep with the pinned CSharpier 1.3.0 tool. Whitespace and
line-wrapping only; OpenNest.Engine.Tests (109) and OpenNest.IO.Tests
pass after reformat, full solution builds 0 errors.

Added .csharpierignore so csproj/config XML keeps its existing layout
(CSharpier's XML wrapping churns attributes with zero benefit).

Formatting is now enforceable: dotnet csharpier check . passes.

OpenNest.Benchmark/BenchmarkJob.cs

@@ -1,7 +1,7 @@
-using OpenNest.Geometry;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using OpenNest.Geometry;
 
 namespace OpenNest.Benchmark
 {
@@ -48,13 +48,28 @@ namespace OpenNest.Benchmark
         /// engine owns its own multi-plate/size strategy; this harness no
         /// longer picks plate sizes on the engine's behalf.
         /// </summary>
-        public NestJob BuildNestJob(int maxPlates, double salvageRate = 0, double minimumSalvageDimension = 0)
+        public NestJob BuildNestJob(
+            int maxPlates,
+            double salvageRate = 0,
+            double minimumSalvageDimension = 0
+        )
         {
             var parts = Requests.Select(r =>
-                DrawingJobMapper.FromDrawing(r.Drawing.Id.ToString(), r.Drawing, r.Quantity));
-            var stock = CandidateSizes.Select(size =>
-                new NestPlateStock(size.ToString(1), size, null, PartSpacing, EdgeSpacing, Quadrant));
-            return new NestJob(parts, stock, new NestJobOptions("Default", maxPlates, salvageRate, minimumSalvageDimension));
+                DrawingJobMapper.FromDrawing(r.Drawing.Id.ToString(), r.Drawing, r.Quantity)
+            );
+            var stock = CandidateSizes.Select(size => new NestPlateStock(
+                size.ToString(1),
+                size,
+                null,
+                PartSpacing,
+                EdgeSpacing,
+                Quadrant
+            ));
+            return new NestJob(
+                parts,
+                stock,
+                new NestJobOptions("Default", maxPlates, salvageRate, minimumSalvageDimension)
+            );
         }
     }
 }