refactor : 重构代码

Assets/YooAsset/Runtime/DownloadSystem/DefaultDownloadRequest/UnityWebRequestAssetBundleDownloader.cs

@@ -76,7 +76,7 @@ namespace YooAsset
             else
             {
                 if (string.IsNullOrEmpty(_args.FileHash))
-                    throw new YooInternalException("File hash is null or empty!");
+                    throw new YooInternalException("File hash is null or empty.");
 
                 // 使用 Unity 缓存
                 // 说明：The file hash defining the version of the asset bundle.

Assets/YooAsset/Runtime/DownloadSystem/DefaultDownloadRequest/UnityWebRequestDownloaderBase.cs

@@ -99,7 +99,7 @@ namespace YooAsset
                     if (_webRequest == null)
                     {
                         Status = EDownloadRequestStatus.Failed;
-                        Error = $"[{GetType().Name}] Created web request is null!";
+                        Error = $"[{GetType().Name}] Created web request is null.";
                     }
                     else
                     {
@@ -226,7 +226,7 @@ namespace YooAsset
         protected void ApplyRequestOptions(int timeout, int watchdogTime, Dictionary<string, string> headers)
         {
             if (_webRequest == null)
-                throw new YooInternalException("Web request is null!");
+                throw new YooInternalException("Web request is null.");
 
             // 设置看门狗超时时间
             _watchdogTime = watchdogTime;