feat: 添加测试服务及相关测试用例，重构 demo 服务逻辑

templates/project/app/services/test.go.tpl

@@ -0,0 +1,10 @@
+package services
+
+import "context"
+
+// @provider
+type test struct{}
+
+func (t *test) Test(ctx context.Context) (string, error) {
+	return "Test", nil
+}