完善所以c#相关的文档和代码

codes/csharp/chapter_stack_and_queue/stack.cs

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+
+using NUnit.Framework;
+using System.Collections.Immutable;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+    public class stack
+    {
+        [Test]
+        public void Test()
+        {
+            /* 初始化栈 */
+            Stack<int> stack = new();
+
+            /* 元素入栈 */
+            stack.Push(1);
+            stack.Push(3);
+            stack.Push(2);
+            stack.Push(5);
+            stack.Push(4);
+            Console.WriteLine("栈 stack = " + String.Join(",", stack.ToImmutableArray()));
+
+            /* 访问栈顶元素 */
+            int peek = stack.Peek();
+            Console.WriteLine("栈顶元素 peek = " + peek);
+
+            /* 元素出栈 */
+            int pop = stack.Pop();
+            Console.WriteLine("出栈元素 pop = " + pop + "，出栈后 stack = " + String.Join(",", stack.ToImmutableArray()));
+
+            /* 获取栈的长度 */
+            int size = stack.Count();
+            Console.WriteLine("栈的长度 size = " + size);
+
+            /* 判断是否为空 */
+            bool isEmpty = stack.Count() == 0;
+            Console.WriteLine("栈是否为空 = " + isEmpty);
+        }
+    }
+}