refactor(PepLib.Core): move Node classes to Utilities namespace

Node and KeyNode are INI parsing helpers used by IniConfig,
not geometry types. Move from Geometry/ to Utilities/.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PepLib.Core/Utilities/IniConfig.cs

@@ -1,5 +1,3 @@
-using PepLib.Geometry;
-
 namespace PepLib.Utilities
 {
     public class IniConfig

PepLib.Core/Utilities/Node.cs

@@ -1,4 +1,4 @@
-namespace PepLib.Geometry
+namespace PepLib.Utilities
 {
     public class Node
     {