feat: add ColumnAttribute and CellExtensions for BOM parsing

OpenNest.IO/Bom/CellExtensions.cs

@@ -0,0 +1,23 @@
+using ClosedXML.Excel;
+
+namespace OpenNest.IO.Bom
+{
+    public static class CellExtensions
+    {
+        public static int? ToIntOrNull(this IXLCell cell)
+        {
+            if (cell.IsEmpty()) return null;
+            if (cell.DataType == XLDataType.Number) return (int)cell.GetDouble();
+            if (int.TryParse(cell.GetString(), out var i)) return i;
+            return null;
+        }
+
+        public static double? ToDoubleOrNull(this IXLCell cell)
+        {
+            if (cell.IsEmpty()) return null;
+            if (cell.DataType == XLDataType.Number) return cell.GetDouble();
+            if (double.TryParse(cell.GetString(), out var result)) return result;
+            return null;
+        }
+    }
+}

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; }
+    }
+}