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/RoundedRectangleShapeTests.cs

@@ -7,7 +7,12 @@ public class RoundedRectangleShapeTests
     [Fact]
     public void GetDrawing_BoundingBoxMatchesDimensions()
     {
-        var shape = new RoundedRectangleShape { Length = 20, Width = 10, Radius = 2 };
+        var shape = new RoundedRectangleShape
+        {
+            Length = 20,
+            Width = 10,
+            Radius = 2,
+        };
         var drawing = shape.GetDrawing();
 
         var bbox = drawing.Program.BoundingBox();
@@ -18,7 +23,12 @@ public class RoundedRectangleShapeTests
     [Fact]
     public void GetDrawing_AreaIsLessThanFullRectangle()
     {
-        var shape = new RoundedRectangleShape { Length = 20, Width = 10, Radius = 2 };
+        var shape = new RoundedRectangleShape
+        {
+            Length = 20,
+            Width = 10,
+            Radius = 2,
+        };
         var drawing = shape.GetDrawing();
 
         // Area should be less than 20*10=200 because corners are rounded
@@ -30,7 +40,12 @@ public class RoundedRectangleShapeTests
     [Fact]
     public void GetDrawing_ZeroRadius_MatchesRectangleArea()
     {
-        var shape = new RoundedRectangleShape { Length = 20, Width = 10, Radius = 0 };
+        var shape = new RoundedRectangleShape
+        {
+            Length = 20,
+            Width = 10,
+            Radius = 0,
+        };
         var drawing = shape.GetDrawing();
 
         Assert.Equal(200, drawing.Area, 0.5);