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.Core/CNC/CuttingStrategy/LeadOuts/LeadOut.cs

@@ -1,11 +1,14 @@
-using OpenNest.Geometry;
 using System.Collections.Generic;
+using OpenNest.Geometry;
 
 namespace OpenNest.CNC.CuttingStrategy
 {
     public abstract class LeadOut
     {
-        public abstract List<ICode> Generate(Vector contourEndPoint, double contourNormalAngle,
-            RotationType winding = RotationType.CW);
+        public abstract List<ICode> Generate(
+            Vector contourEndPoint,
+            double contourNormalAngle,
+            RotationType winding = RotationType.CW
+        );
     }
 }