调整工具类的方法，优化方法调用及增加迁移工具及其用法

examples/storage_example.go

@@ -36,8 +36,20 @@ func main() {
 		proxyHandler := storage.NewProxyHandler(ossStorage)
 
 		// 创建中间件链
+		var corsConfig *middleware.CORSConfig
+		if cfg.GetCORS() != nil {
+			c := cfg.GetCORS()
+			corsConfig = middleware.NewCORSConfig(
+				c.AllowedOrigins,
+				c.AllowedMethods,
+				c.AllowedHeaders,
+				c.ExposedHeaders,
+				c.AllowCredentials,
+				c.MaxAge,
+			)
+		}
 		chain := middleware.NewChain(
-			middleware.CORS(cfg.GetCORS()),
+			middleware.CORS(corsConfig),
 			middleware.Timezone,
 		)