fix(config): 修复 Etcd客户端初始化和清理逻辑

- 在 NewEtcdClientWithCleanup 函数中增加对 etcdClient 是否为 nil 的判断
- 如果 etcdClient 为 nil，返回空的 cleanup 函数，避免潜在的空指针异常
-优化 cleanup 函数的定义，提高代码可读性

config/etcd_client.go

@@ -37,8 +37,9 @@ func NewEtcdClient(startup *initutils.Startup) *clientv3.Client {
 
 func NewEtcdClientWithCleanup(startup *initutils.Startup) (*clientv3.Client, func()) {
 	etcdClient := NewEtcdClient(startup)
-	cleanup := func() {
-		etcdClient.Close()
+	if etcdClient == nil {
+		return nil, func() {}
 	}
+	cleanup := func() { etcdClient.Close() }
 	return etcdClient, cleanup
 }