feat: 重构消息处理模块，引入统一的消息接口和类型安全的消息解析

util/url.go

@@ -36,11 +36,10 @@ func normalizeURL(rawURL string) string {
 	return u.String()
 }
 
-func DownloadFile(url string, filepath string) error {
+func DownloadFile(url string, filepath string) (err error) {
 	// 发送 HTTP GET 请求
 	// resp, err := http.Get(url)
 	var resp *http.Response
-	var err error
 	var maxRetry = 100
 	var retry = 0
 	for resp, err = http.Get(url); err != nil && retry < maxRetry; resp, err = http.Get(url) {