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/BestFit/BestFitOverlapTests.cs

@@ -58,9 +58,11 @@ public class BestFitOverlapTests
             if (parts[0].Intersects(parts[1], out var pts))
             {
                 overlapping++;
-                _output.WriteLine($"  OVERLAP #{overlapping}: Test {result.Candidate.TestNumber} " +
-                    $"Part2Rot={OpenNest.Math.Angle.ToDegrees(result.Candidate.Part2Rotation):F1}° " +
-                    $"collision pts={pts.Count}");
+                _output.WriteLine(
+                    $"  OVERLAP #{overlapping}: Test {result.Candidate.TestNumber} "
+                        + $"Part2Rot={OpenNest.Math.Angle.ToDegrees(result.Candidate.Part2Rotation):F1}° "
+                        + $"collision pts={pts.Count}"
+                );
             }
         }
 

OpenNest.Tests/BestFit/BestFitResultFrameTests.cs

@@ -16,8 +16,10 @@ public class BestFitResultFrameTests
 
         var result = EvaluateOffsetPair(canonical, new Vector(40, 30));
 
-        Assert.True(IsNonAxisAligned(result.OptimalRotation),
-            $"Expected a non-axis-aligned result, got {Angle.ToDegrees(result.OptimalRotation):F2} degrees.");
+        Assert.True(
+            IsNonAxisAligned(result.OptimalRotation),
+            $"Expected a non-axis-aligned result, got {Angle.ToDegrees(result.OptimalRotation):F2} degrees."
+        );
 
         var parts = result.BuildCanonicalParts();
         var bounds = result.GetCutBounds(parts);
@@ -55,7 +57,7 @@ public class BestFitResultFrameTests
             Part1Rotation = 0,
             Part2Rotation = System.Math.PI,
             Part2Offset = offset,
-            Spacing = 0.25
+            Spacing = 0.25,
         };
 
         return new PairEvaluator().Evaluate(candidate);

OpenNest.Tests/BestFit/NfpBestFitIntegrationTests.cs

@@ -38,9 +38,7 @@ public class NfpBestFitIntegrationTests
         var drawing = TestHelpers.MakeLShapeDrawing();
         var results = finder.FindBestFits(drawing);
 
-        var bestUtilization = results
-            .Where(r => r.Keep)
-            .Max(r => r.Utilization);
+        var bestUtilization = results.Where(r => r.Keep).Max(r => r.Utilization);
         Assert.True(bestUtilization > 0.5);
     }
 
@@ -51,7 +49,6 @@ public class NfpBestFitIntegrationTests
         var drawing = TestHelpers.MakeSquareDrawing();
         var results = finder.FindBestFits(drawing);
 
-        Assert.All(results.Where(r => r.Keep), r =>
-            Assert.Equal("Valid", r.Reason));
+        Assert.All(results.Where(r => r.Keep), r => Assert.Equal("Valid", r.Reason));
     }
 }

OpenNest.Tests/BestFit/NfpSlideStrategyTests.cs

@@ -119,6 +119,9 @@ public class NfpSlideStrategyTests
                 validCount++;
         }
 
-        Assert.True(validCount > 0, $"No non-overlapping candidates found out of {candidates.Count} total. Candidate 0 offset: {candidates[0].Part2Offset}");
+        Assert.True(
+            validCount > 0,
+            $"No non-overlapping candidates found out of {candidates.Count} total. Candidate 0 offset: {candidates[0].Part2Offset}"
+        );
     }
 }