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_Tests/ExcelDocsComparerTests.cs

@@ -0,0 +1,59 @@
+using ClosedXML_Examples;
+using NUnit.Framework;
+using System.IO;
+
+namespace ClosedXML_Tests
+{
+    [TestFixture]
+    public class ExcelDocsComparerTests
+    {
+        [Test]
+        public void CheckEqual()
+        {
+            string left = ExampleHelper.GetTempFilePath("left.xlsx");
+            string right = ExampleHelper.GetTempFilePath("right.xlsx");
+            try
+            {
+                new BasicTable().Create(left);
+                new BasicTable().Create(right);
+                Assert.IsTrue(ExcelDocsComparer.Compare(left, right, out string message));
+            }
+            finally
+            {
+                if (File.Exists(left))
+                {
+                    File.Delete(left);
+                }
+                if (File.Exists(right))
+                {
+                    File.Delete(right);
+                }
+            }
+        }
+
+        [Test]
+        public void CheckNonEqual()
+        {
+            string left = ExampleHelper.GetTempFilePath("left.xlsx");
+            string right = ExampleHelper.GetTempFilePath("right.xlsx");
+            try
+            {
+                new BasicTable().Create(left);
+                new HelloWorld().Create(right);
+
+                Assert.IsFalse(ExcelDocsComparer.Compare(left, right, out string message));
+            }
+            finally
+            {
+                if (File.Exists(left))
+                {
+                    File.Delete(left);
+                }
+                if (File.Exists(right))
+                {
+                    File.Delete(right);
+                }
+            }
+        }
+    }
+}