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/Jobs/NestJobProgress.cs

@@ -1,10 +1,20 @@
 namespace OpenNest;
 
-public enum NestJobStage { EvaluatingCandidate, PlateCommitted }
+public enum NestJobStage
+{
+    EvaluatingCandidate,
+    PlateCommitted,
+}
 
 /// <summary>
 /// Whole-job progress. Counts change only after a physical sheet commits; LegacyProgress is optional
 /// non-authoritative detail from a plate nester while its candidate remains under evaluation.
 /// </summary>
-public sealed record NestJobProgress(NestJobStage Stage, string StockId, int PlateIndex,
-    int CommittedPlates, int CommittedParts, NestProgress LegacyProgress = null);
+public sealed record NestJobProgress(
+    NestJobStage Stage,
+    string StockId,
+    int PlateIndex,
+    int CommittedPlates,
+    int CommittedParts,
+    NestProgress LegacyProgress = null
+);