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/Examples/ImageHandlingTests.cs

@@ -0,0 +1,21 @@
+using ClosedXML_Examples;
+using NUnit.Framework;
+
+namespace ClosedXML_Tests.Examples
+{
+    [TestFixture]
+    public class ImageHandlingTests
+    {
+        [Test]
+        public void ImageAnchors()
+        {
+            TestHelper.RunTestExample<ImageAnchors>(@"ImageHandling\ImageAnchors.xlsx");
+        }
+
+        [Test]
+        public void ImageFormats()
+        {
+            TestHelper.RunTestExample<ImageFormats>(@"ImageHandling\ImageFormats.xlsx");
+        }
+    }
+}