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/BestFit/IDistanceComputer.cs

@@ -1,5 +1,5 @@
-using OpenNest.Geometry;
 using System.Collections.Generic;
+using OpenNest.Geometry;
 
 namespace OpenNest.Engine.BestFit
 {
@@ -8,11 +8,13 @@ namespace OpenNest.Engine.BestFit
         double[] ComputeDistances(
             List<Line> stationaryLines,
             List<Line> movingTemplateLines,
-            SlideOffset[] offsets);
+            SlideOffset[] offsets
+        );
 
         double[] ComputeDistances(
             List<Entity> stationaryEntities,
             List<Entity> movingEntities,
-            SlideOffset[] offsets);
+            SlideOffset[] offsets
+        );
     }
 }