feat(benchmark): add --progress logging for engine solves

Long whole-job solves ran silently, so there was no way to tell a slow
engine from a hung one until the timeout fired. --progress hands each
solve a JobProgressLog that prints [job/engine] lines for start, finish
(or failure/timeout), every plate commit, and candidate evaluations
throttled to one line per 2 s so parallel runs stay readable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Benchmark/Program.cs

@@ -123,7 +123,8 @@ static class BenchmarkConsole
             options.SalvageRate,
             options.MinimumSalvageDimension,
             options.OutputDirectory,
-            options.Parallel
+            options.Parallel,
+            options.Progress ? Console.Out : null
         );
 
         Report.PrintDetailed(results);
@@ -196,6 +197,10 @@ static class BenchmarkConsole
                         );
                     break;
 
+                case "--progress":
+                    o.Progress = true;
+                    break;
+
                 case "--help":
                     PrintUsage();
                     return null;
@@ -322,6 +327,9 @@ static class BenchmarkConsole
         Console.Error.WriteLine(
             "                                 which gives the cleanest per-engine timings)"
         );
+        Console.Error.WriteLine(
+            "  --progress                      Log each solve's start, engine progress and finish"
+        );
         Console.Error.WriteLine("  --help                          Show this message");
     }
 
@@ -336,5 +344,6 @@ static class BenchmarkConsole
         public double? SalvageRate;
         public double? MinimumSalvageDimension;
         public int Parallel = 3;
+        public bool Progress;
     }
 }