fix: use GORM v2 row locking for subscription resets (#6057)

* fix: use GORM v2 row locking for subscription resets

* docs: codify GORM row locking rules

model/subscription.go

@@ -1027,7 +1027,7 @@ func adminResetUserSubscriptionsByPlanTx(tx *gorm.DB, userId int, plan *Subscrip
 		return nil, errors.New("invalid reset args")
 	}
 	var subs []UserSubscription
-	if err := tx.Set("gorm:query_option", "FOR UPDATE").
+	if err := lockForUpdate(tx).
 		Where("user_id = ? AND plan_id = ? AND status = ? AND end_time > ?", userId, plan.Id, "active", now).
 		Order("end_time asc, id asc").
 		Find(&subs).Error; err != nil {
@@ -1049,7 +1049,7 @@ func adminResetPlanSubscriptionsTx(tx *gorm.DB, plan *SubscriptionPlan, now int6
 		return nil, errors.New("invalid reset args")
 	}
 	var subs []UserSubscription
-	if err := tx.Set("gorm:query_option", "FOR UPDATE").
+	if err := lockForUpdate(tx).
 		Where("plan_id = ? AND status = ? AND end_time > ?", plan.Id, "active", now).
 		Order("user_id asc, end_time asc, id asc").
 		Find(&subs).Error; err != nil {