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/FormulasWithEvaluation.cs

@@ -0,0 +1,16 @@
+using ClosedXML.Excel;
+
+namespace ClosedXML_Examples.Misc
+{
+    public class FormulasWithEvaluation : Formulas
+    {
+        public override void Create(string filePath)
+        {
+            base.Create(filePath);
+            using (var wb = new XLWorkbook(filePath))
+            {
+                wb.Save(true, true);
+            }
+        }
+    }
+}