Initial commit of the ClosedXML library

Establishes the foundational structure, core Excel functionality, and tooling.

- Implements base components for cells, ranges, columns, and rows.
- Integrates a custom calculation engine with a wide range of Excel functions.
- Adds comprehensive support for styling, conditional formatting, data validation, comments, pictures, and charts.
- Configures build setup, project metadata (NuGet), and developer guidelines.
- Includes editor and Git attributes for consistent code style and line endings.

ClosedXML_Examples/Styles/StyleNumberFormat.cs

@@ -0,0 +1,85 @@
+using System;
+using ClosedXML.Excel;
+
+namespace ClosedXML_Examples.Styles
+{
+    public class StyleNumberFormat : IXLExample
+    {
+        #region Variables
+
+        // Public
+
+        // Private
+
+
+        #endregion
+
+        #region Properties
+
+        // Public
+
+        // Private
+
+        // Override
+
+
+        #endregion
+
+        #region Constructors
+
+        // Public
+        public StyleNumberFormat()
+        {
+
+        }
+
+
+        // Private
+
+
+        #endregion
+
+        #region Events
+
+        // Public
+
+        // Private
+
+        // Override
+
+
+        #endregion
+
+        #region Methods
+
+        // Public
+        public void Create(String filePath)
+        {
+            var workbook = new XLWorkbook();
+            var ws = workbook.Worksheets.Add("Style NumberFormat");
+
+            var co = 2;
+            var ro = 1;
+
+            ws.Cell(++ro, co).Value = "123456.789";
+            ws.Cell(ro, co).Style.NumberFormat.Format = "$ #,##0.00";
+
+            ws.Cell(++ro, co).Value = "12.345";
+            ws.Cell(ro, co).Style.NumberFormat.Format = "0000";
+
+            ws.Cell(++ro, co).Value = "12.345";
+            ws.Cell(ro, co).Style.NumberFormat.NumberFormatId = 3;
+
+            ws.Column(co).AdjustToContents();
+
+            workbook.SaveAs(filePath);
+        }
+
+        // Private
+
+        // Override
+
+
+        #endregion
+    }
+}