Move math utilities to OpenNest.Math namespace

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

OpenNest.Core/NestConstraints.cs

@@ -1,4 +1,5 @@
 using System;
+using OpenNest.Math;
 
 namespace OpenNest
 {
@@ -37,7 +38,7 @@ namespace OpenNest
             if (diff.IsEqualTo(Angle.TwoPI))
                 return false;
 
-            if ((diff > Math.PI || diff.IsEqualTo(Math.PI)) && Allow180Equivalent)
+            if ((diff > System.Math.PI || diff.IsEqualTo(System.Math.PI)) && Allow180Equivalent)
                 return false;
 
             return true;