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/Misc/WorkbookProtection.cs

@@ -0,0 +1,23 @@
+using System;
+using ClosedXML.Excel;
+
+namespace ClosedXML_Examples.Misc
+{
+    public class WorkbookProtection : IXLExample
+    {
+        #region Methods
+
+        // Public
+        public void Create(String filePath)
+        {
+            using (var wb = new XLWorkbook())
+            {
+                var ws = wb.Worksheets.Add("Workbook Protection");
+                wb.Protect(true, false, "Abc@123");
+                wb.SaveAs(filePath);
+            }
+        }
+
+        #endregion
+    }
+}