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.Engine/Jobs/PlateNesterFactory.cs

@@ -1,4 +1,5 @@
 using System;
+
 namespace OpenNest;
 
 /// <summary>
@@ -16,9 +17,13 @@ public static class PlateNesterFactory
         {
             "Default" => new DefaultPlateNester(),
             "Strip" => new StripPlateNester(),
-            "Vertical Remnant" => new LegacyPlateNesterAdapter(plate => new VerticalRemnantEngine(plate)),
-            "Horizontal Remnant" => new LegacyPlateNesterAdapter(plate => new HorizontalRemnantEngine(plate)),
-            _ => throw new NotSupportedException($"Unknown placement strategy: {strategy}.")
+            "Vertical Remnant" => new LegacyPlateNesterAdapter(plate => new VerticalRemnantEngine(
+                plate
+            )),
+            "Horizontal Remnant" => new LegacyPlateNesterAdapter(
+                plate => new HorizontalRemnantEngine(plate)
+            ),
+            _ => throw new NotSupportedException($"Unknown placement strategy: {strategy}."),
         };
     }
 }