refactor the runtime code

重构了运行时代码，支持全新的文件系统。

Assets/YooAsset/Runtime/DownloadSystem/WebRequestCounter.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace YooAsset
+{
+    internal class WebRequestCounter
+    {
+        /// <summary>
+        /// 记录网络请求失败事件的次数
+        /// </summary>
+        private static readonly Dictionary<string, int> _requestFailedRecorder = new Dictionary<string, int>(1000);
+
+        /// <summary>
+        /// 记录请求失败事件
+        /// </summary>
+        public static void RecordRequestFailed(string packageName, string eventName)
+        {
+            string key = $"{packageName}_{eventName}";
+            if (_requestFailedRecorder.ContainsKey(key) == false)
+                _requestFailedRecorder.Add(key, 0);
+            _requestFailedRecorder[key]++;
+        }
+
+        /// <summary>
+        /// 获取请求失败的次数
+        /// </summary>
+        public static int GetRequestFailedCount(string packageName, string eventName)
+        {
+            string key = $"{packageName}_{eventName}";
+            if (_requestFailedRecorder.ContainsKey(key) == false)
+                _requestFailedRecorder.Add(key, 0);
+            return _requestFailedRecorder[key];
+        }
+    }
+}