Move math utilities to OpenNest.Math namespace

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

OpenNest.Core/Math/Tolerance.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace OpenNest.Math
+{
+    public static class Tolerance
+    {
+        public const double Epsilon = 0.00001;
+
+        public static bool IsEqualTo(this double a, double b, double tolerance = Epsilon)
+        {
+            return System.Math.Abs(b - a) <= tolerance;
+        }
+    }
+}