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.Api/NestRequest.cs

@@ -6,17 +6,20 @@ namespace OpenNest.Api;
 public class NestRequest
 {
     public IReadOnlyList<NestRequestPart> Parts { get; init; } = [];
+
     /// <summary>
     /// Explicit available physical stock. Null keeps the legacy unlimited SheetSize fallback;
     /// an empty list deliberately means no stock is available.
     /// </summary>
     public IReadOnlyList<NestRequestPlate> Plates { get; init; }
     public Size SheetSize { get; init; } = new(60, 120);
+
     /// <summary>Built-in whole-job placement strategy. Explicit values take precedence over legacy Strategy.</summary>
     public string PlacementStrategy { get; init; } = "Default";
     public string Material { get; init; } = "Steel, A1011 HR";
     public double Thickness { get; init; } = 0.06;
     public double Spacing { get; init; } = 0.1;
+
     /// <summary>Legacy compatibility setting; Auto maps to the Default whole-job strategy.</summary>
     public NestStrategy Strategy { get; init; } = NestStrategy.Auto;
     public CutParameters Cutting { get; init; } = CutParameters.Default;