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.

resources/logo/favicon-01.svg

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Generator: Adobe Illustrator 15.1.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 width="1000px" height="1000px" viewBox="0 0 1000 1000" enable-background="new 0 0 1000 1000" xml:space="preserve">
+<path fill="#4CAF50" d="M900.006,235.659v528.718C900.006,839.275,839.278,900,764.35,900H235.661
+	c-74.926,0-135.667-60.725-135.667-135.623V235.659C99.994,160.727,160.735,100,235.661,100H764.35
+	C839.278,100,900.006,160.727,900.006,235.659z"/>
+<path opacity="0.2" fill="#4CAF50" d="M900.006,482.063v282.313C900.006,839.275,839.278,900,764.35,900H482.04L184.244,602.203
+	l417.928-417.966L900.006,482.063z"/>
+<g>
+	<polygon fill="#FFFFFF" points="448.557,500.016 265.304,683.27 184.926,602.881 368.185,419.633 	"/>
+	<polygon fill="#FFFFFF" points="580.38,631.823 397.114,815.082 316.744,734.709 499.997,551.446 	"/>
+	<polygon fill="#FFFFFF" points="683.264,265.306 499.997,448.57 419.62,368.197 602.882,184.928 	"/>
+	<polygon fill="#FFFFFF" points="815.077,397.119 631.816,580.394 551.44,500.016 734.699,316.754 	"/>
+</g>
+</svg>