refactor: move err all servers down to error.go (#189)

Signed-off-by: ZhangJian He <shoothzj@gmail.com>

Author: hezhangjian

opengemini/error.go

@@ -17,12 +17,13 @@ package opengemini
 import "errors"
 
 var (
+	ErrAllServersDown    = errors.New("all servers down")
 	ErrEmptyDatabaseName = errors.New("empty database name")
-	ErrRetentionPolicy   = errors.New("empty retention policy")
 	ErrEmptyMeasurement  = errors.New("empty measurement")
 	ErrEmptyCommand      = errors.New("empty command")
 	ErrEmptyTagOrField   = errors.New("empty tag or field")
 	ErrEmptyTagKey       = errors.New("empty tag key")
+	ErrRetentionPolicy   = errors.New("empty retention policy")
 )
 
 // checkDatabaseName checks if the database name is empty and returns an error if it is.

opengemini/servers_check.go

@@ -16,13 +16,10 @@ package opengemini
 
 import (
 	"context"
-	"errors"
 	"sync"
 	"time"
 )
 
-var ErrAllServersDown = errors.New("all servers down")
-
 const (
 	healthCheckPeriod = time.Second * 10
 )