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/Cincinnati/SpeedClassifierTests.cs

@@ -9,7 +9,11 @@ public class SpeedClassifierTests
     [InlineData(5.0, 10.0, "FAST")]
     [InlineData(4.9, 10.0, "MEDIUM")]
     [InlineData(0.5, 10.0, "SLOW")]
-    public void Classify_ReturnsExpectedClass(double contourLength, double sheetDiagonal, string expected)
+    public void Classify_ReturnsExpectedClass(
+        double contourLength,
+        double sheetDiagonal,
+        string expected
+    )
     {
         var classifier = new SpeedClassifier();
         Assert.Equal(expected, classifier.Classify(contourLength, sheetDiagonal));
@@ -19,7 +23,11 @@ public class SpeedClassifierTests
     [InlineData(0.8702, 3.927, "CutDist=.8702/3.927")]
     [InlineData(18.9722, 3.927, "CutDist=18.9722/3.927")]
     [InlineData(0.0, 10.0, "CutDist=0/10")]
-    public void FormatCutDist_IncludesLengthAndDiagonal(double contour, double diag, string expected)
+    public void FormatCutDist_IncludesLengthAndDiagonal(
+        double contour,
+        double diag,
+        string expected
+    )
     {
         var classifier = new SpeedClassifier();
         Assert.Equal(expected, classifier.FormatCutDist(contour, diag));