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/Sequencing/AdvancedSequencerTests.cs

@@ -24,7 +24,7 @@ public class AdvancedSequencerTests
         {
             Method = SequenceMethod.Advanced,
             MinDistanceBetweenRowsColumns = 5.0,
-            AlternateRowsColumns = false
+            AlternateRowsColumns = false,
         };
         var sequencer = new AdvancedSequencer(parameters);
         var result = sequencer.Sequence(plate.Parts.ToList(), plate);
@@ -52,7 +52,7 @@ public class AdvancedSequencerTests
         {
             Method = SequenceMethod.Advanced,
             MinDistanceBetweenRowsColumns = 5.0,
-            AlternateRowsColumns = true
+            AlternateRowsColumns = true,
         };
         var sequencer = new AdvancedSequencer(parameters);
         var result = sequencer.Sequence(plate.Parts.ToList(), plate);