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.Tests/Shapes/NgonShapeTests.cs

@@ -31,9 +31,7 @@ public class NgonShapeTests
         var shape = new NgonShape { Sides = sides, Width = 20 };
         var drawing = shape.GetDrawing();
 
-        var moves = drawing.Program.Codes
-            .OfType<OpenNest.CNC.LinearMove>()
-            .Count();
+        var moves = drawing.Program.Codes.OfType<OpenNest.CNC.LinearMove>().Count();
         Assert.Equal(sides, moves);
     }
 
@@ -43,9 +41,7 @@ public class NgonShapeTests
         var shape = new NgonShape { Sides = 2, Width = 20 };
         var drawing = shape.GetDrawing();
 
-        var moves = drawing.Program.Codes
-            .OfType<OpenNest.CNC.LinearMove>()
-            .Count();
+        var moves = drawing.Program.Codes.OfType<OpenNest.CNC.LinearMove>().Count();
         Assert.Equal(3, moves);
     }
 }