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/Excel/Worksheets/XLSheetViewTests.cs

@@ -0,0 +1,73 @@
+// Keep this file CodeMaid organised and cleaned
+using ClosedXML.Excel;
+using NUnit.Framework;
+using System;
+using System.IO;
+using System.Linq;
+
+namespace ClosedXML_Tests.Excel.Worksheets
+{
+    [TestFixture]
+    public class XLSheetViewTests
+    {
+        [Test]
+        public void CopyWorksheetSheetViews()
+        {
+            using var wb1 = new XLWorkbook();
+            using var wb2 = new XLWorkbook();
+
+            var ws1 = wb1.AddWorksheet("WS1");
+            ws1.SheetView.TopLeftCellAddress = ws1.Cell("AZ2000").Address;
+
+            var ws2 = ws1.CopyTo(wb2, "WS2");
+
+            Assert.AreEqual(ws2, ws2.SheetView.Worksheet);
+            Assert.AreEqual("AZ2000", ws2.SheetView.TopLeftCellAddress.ToString());
+        }
+
+        [Test]
+        public void InvalidTopLeftCell()
+        {
+            using var wb = new XLWorkbook();
+            var ws1 = wb.AddWorksheet();
+            var ws2 = wb.AddWorksheet();
+
+            Assert.Throws<ArgumentException>(() => ws1.SheetView.TopLeftCellAddress = ws2.Cell("A1").Address);
+        }
+
+        [Test]
+        public void SheetViews()
+        {
+            using var ms = new MemoryStream();
+            using (var wb = new XLWorkbook())
+            {
+                var ws = wb.AddWorksheet();
+                ws.SheetView.TopLeftCellAddress = ws.Cell("AZ2000").Address;
+                wb.SaveAs(ms);
+            }
+
+            ms.Seek(0, SeekOrigin.Begin);
+
+            using (var wb = new XLWorkbook(ms))
+            {
+                var ws = wb.Worksheets.First();
+                Assert.AreEqual("AZ2000", ws.SheetView.TopLeftCellAddress.ToString());
+
+                ws.SheetView.TopLeftCellAddress = ws.Cell("AZ2000")
+                    .CellBelow()
+                    .CellRight()
+                    .Address;
+
+                wb.Save();
+            }
+
+            ms.Seek(0, SeekOrigin.Begin);
+
+            using (var wb = new XLWorkbook(ms))
+            {
+                var ws = wb.Worksheets.First();
+                Assert.AreEqual("BA2001", ws.SheetView.TopLeftCellAddress.ToString());
+            }
+        }
+    }
+}