fix(csharp): reformat csharp codes and docs (#652)

* fix(csharp): reformat the C# codes and docs

* Update time_complexity.md

---------

Co-authored-by: Yudong Jin <krahets@163.com>

docs/chapter_hashing/hash_map.md

@@ -368,18 +368,15 @@
     ```csharp title="hash_map.cs"
     /* 遍历哈希表 */
     // 遍历键值对 Key->Value
-    foreach (var kv in map)
-    {
+    foreach (var kv in map) {
         Console.WriteLine(kv.Key + " -> " + kv.Value);
     }
     // 单独遍历键 key
-    foreach (int key in map.Keys)
-    {
+    foreach (int key in map.Keys) {
         Console.WriteLine(key);
     }
     // 单独遍历值 value
-    foreach (String val in map.Values)
-    {
+    foreach (String val in map.Values) {
         Console.WriteLine(val);
     }
     ```