feat: add ColumnAttribute and CellExtensions for BOM parsing

OpenNest.IO/Bom/ColumnAttribute.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace OpenNest.IO.Bom
+{
+    [AttributeUsage(AttributeTargets.Property)]
+    public class ColumnAttribute : Attribute
+    {
+        public ColumnAttribute(params string[] names)
+        {
+            Names = names;
+        }
+
+        public string[] Names { get; }
+    }
+}