feat: add SpeedClassifier for FAST/MEDIUM/SLOW cut distance classification

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest.Posts.Cincinnati/SpeedClassifier.cs

@@ -0,0 +1,31 @@
+namespace OpenNest.Posts.Cincinnati
+{
+    public sealed class SpeedClassifier
+    {
+        public double FastThreshold { get; set; } = 0.5;
+        public double SlowThreshold { get; set; } = 0.1;
+
+        public string Classify(double contourLength, double sheetDiagonal)
+        {
+            var ratio = contourLength / sheetDiagonal;
+            if (ratio > FastThreshold) return "FAST";
+            if (ratio <= SlowThreshold) return "SLOW";
+            return "MEDIUM";
+        }
+
+        public string FormatCutDist(double contourLength, double sheetDiagonal)
+        {
+            return $"CutDist={FormatValue(contourLength)}/{FormatValue(sheetDiagonal)}";
+        }
+
+        private static string FormatValue(double value)
+        {
+            // Cincinnati convention: no leading zero for values < 1 (e.g., ".8702" not "0.8702")
+            var rounded = System.Math.Round(value, 4);
+            var str = rounded.ToString("0.####");
+            if (rounded > 0 && rounded < 1 && str.StartsWith("0."))
+                return str.Substring(1);
+            return str;
+        }
+    }
+}