feat: add Pattern class for grouping parts with relative positions

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

OpenNest.Engine/OpenNest.Engine.csproj

@@ -45,6 +45,7 @@
     <Compile Include="NestDirection.cs" />
     <Compile Include="NestEngine.cs" />
     <Compile Include="NestItem.cs" />
+    <Compile Include="Pattern.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="RectanglePacking\Bin.cs" />
     <Compile Include="RectanglePacking\FillBestFit.cs" />

OpenNest.Engine/Pattern.cs

@@ -0,0 +1,57 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest
+{
+    public class Pattern
+    {
+        public Pattern()
+        {
+            Parts = new List<Part>();
+        }
+
+        public List<Part> Parts { get; }
+
+        public Box BoundingBox { get; private set; }
+
+        public void UpdateBounds()
+        {
+            BoundingBox = Parts.GetBoundingBox();
+        }
+
+        public List<Line> GetLines(PushDirection facingDirection)
+        {
+            var lines = new List<Line>();
+
+            foreach (var part in Parts)
+                lines.AddRange(Helper.GetPartLines(part, facingDirection));
+
+            return lines;
+        }
+
+        public List<Line> GetOffsetLines(double spacing, PushDirection facingDirection)
+        {
+            var lines = new List<Line>();
+
+            foreach (var part in Parts)
+                lines.AddRange(Helper.GetOffsetPartLines(part, spacing, facingDirection));
+
+            return lines;
+        }
+
+        public Pattern Clone(Vector offset)
+        {
+            var pattern = new Pattern();
+
+            foreach (var part in Parts)
+            {
+                var clone = (Part)part.Clone();
+                clone.Offset(offset);
+                pattern.Parts.Add(clone);
+            }
+
+            pattern.UpdateBounds();
+            return pattern;
+        }
+    }
+}