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/Strategies/FillPipelineTests.cs

@@ -25,8 +25,10 @@ public class FillPipelineTests
 
         engine.Fill(item, plate.WorkArea(), null, System.Threading.CancellationToken.None);
 
-        Assert.True(engine.PhaseResults.Count >= FillStrategyRegistry.Strategies.Count,
-            $"Expected phase results from all active strategies, got {engine.PhaseResults.Count}");
+        Assert.True(
+            engine.PhaseResults.Count >= FillStrategyRegistry.Strategies.Count,
+            $"Expected phase results from all active strategies, got {engine.PhaseResults.Count}"
+        );
     }
 
     [Fact]
@@ -36,14 +38,21 @@ public class FillPipelineTests
         var engine = new DefaultNestEngine(plate);
         var item = new NestItem { Drawing = MakeRectDrawing(20, 10) };
 
-        var parts = engine.Fill(item, plate.WorkArea(), null, System.Threading.CancellationToken.None);
+        var parts = engine.Fill(
+            item,
+            plate.WorkArea(),
+            null,
+            System.Threading.CancellationToken.None
+        );
 
         Assert.True(parts.Count > 0);
-        Assert.True(engine.WinnerPhase == NestPhase.Pairs ||
-                    engine.WinnerPhase == NestPhase.Linear ||
-                    engine.WinnerPhase == NestPhase.RectBestFit ||
-                    engine.WinnerPhase == NestPhase.Extents ||
-                    engine.WinnerPhase == NestPhase.Custom);
+        Assert.True(
+            engine.WinnerPhase == NestPhase.Pairs
+                || engine.WinnerPhase == NestPhase.Linear
+                || engine.WinnerPhase == NestPhase.RectBestFit
+                || engine.WinnerPhase == NestPhase.Extents
+                || engine.WinnerPhase == NestPhase.Custom
+        );
     }
 
     [Fact]