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/VerticalRemnantEngine.cs

@@ -14,7 +14,8 @@ namespace OpenNest
     /// </summary>
     public class VerticalRemnantEngine : DefaultNestEngine
     {
-        public VerticalRemnantEngine(Plate plate) : base(plate) { }
+        public VerticalRemnantEngine(Plate plate)
+            : base(plate) { }
 
         public override string Name => "Vertical Remnant";
 
@@ -24,9 +25,17 @@ namespace OpenNest
 
         public override NestDirection? PreferredDirection => NestDirection.Horizontal;
 
-        public override List<double> BuildAngles(NestItem item, ClassificationResult classification, Box workArea)
+        public override List<double> BuildAngles(
+            NestItem item,
+            ClassificationResult classification,
+            Box workArea
+        )
         {
-            var baseAngles = new List<double> { classification.PrimaryAngle, classification.PrimaryAngle + Angle.HalfPI };
+            var baseAngles = new List<double>
+            {
+                classification.PrimaryAngle,
+                classification.PrimaryAngle + Angle.HalfPI,
+            };
             baseAngles.Sort((a, b) => RotatedWidth(item, a).CompareTo(RotatedWidth(item, b)));
             return baseAngles;
         }