refactor(db): 增强测试事务支持和保存点管理

- 在 HoTimeDB 中新增测试事务功能，允许在测试模式下使用事务进行操作
- 实现 BeginTestTx 和 RollbackTestTx 方法，支持测试事务的开启和回滚
- 在 Action 方法中集成保存点管理，确保在测试模式下的嵌套事务处理
- 更新 README.md，添加 API 测试框架的相关说明，提升文档完整性

application.go

@@ -1,14 +1,8 @@
 package hotime
 
 import (
-	. "code.hoteas.com/golang/hotime/cache"
-	"code.hoteas.com/golang/hotime/code"
-	. "code.hoteas.com/golang/hotime/common"
-	. "code.hoteas.com/golang/hotime/db"
-	. "code.hoteas.com/golang/hotime/log"
 	"database/sql"
 	"fmt"
-	"github.com/sirupsen/logrus"
 	"io/ioutil"
 	"net/http"
 	"net/url"
@@ -17,6 +11,13 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	. "code.hoteas.com/golang/hotime/cache"
+	"code.hoteas.com/golang/hotime/code"
+	. "code.hoteas.com/golang/hotime/common"
+	. "code.hoteas.com/golang/hotime/db"
+	. "code.hoteas.com/golang/hotime/log"
+	"github.com/sirupsen/logrus"
 )
 
 type Application struct {