refactor(PepLib.Core): reorganize files into logical folder structure

Move 38 files from root directory into organized subfolders:
- Enums/ (7 files): StatusType, ApplicationType, DrawingType, etc.
- Geometry/ (5 files): Vector, Box, Size, Spacing, Node
- Models/ (15 files): Nest, Plate, Part, Program, Report, etc.
- Utilities/ (7 files): MathHelper, Tolerance, ZipHelper, etc.
- Extensions/ (2 files): PartListExtensions, PlateListExtensions
- Interfaces/ (1 file): IMovable

Update namespaces to follow folder hierarchy (e.g., PepLib.Models).
Add GlobalUsings.cs for internal backward compatibility.
Update Codes/ and IO/ files with new using statements.
Update PepApi.Core consumers to reference new namespaces.

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

PepLib.Core/Geometry/Spacing.cs

@@ -0,0 +1,27 @@
+
+namespace PepLib.Geometry
+{
+    public class Spacing
+    {
+        public Spacing()
+            : this(0, 0, 0, 0)
+        {
+        }
+
+        public Spacing(double l, double b, double r, double t)
+        {
+            Left = l;
+            Bottom = b;
+            Right = r;
+            Top = t;
+        }
+
+        public double Left { get; set; }
+
+        public double Bottom { get; set; }
+
+        public double Right { get; set; }
+
+        public double Top { get; set; }
+    }
+}