Move geometry primitives to OpenNest.Geometry namespace

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

OpenNest.Core/Geometry/IBoundable.cs

@@ -0,0 +1,18 @@
+
+namespace OpenNest.Geometry
+{
+    public interface IBoundable
+    {
+        Box BoundingBox { get; }
+
+        double Left { get; }
+
+        double Right { get; }
+
+        double Top { get; }
+
+        double Bottom { get; }
+
+        void UpdateBounds();
+    }
+}