refactor: improve user group handling and add GetUserUsableGroups function

- Introduced a new function `GetUserUsableGroupsCopy` to return a copy of user usable groups.
- Updated `GetUserUsableGroups` to utilize the new function for better encapsulation.
- Changed variable names from `UserUsableGroups` to `userUsableGroups` for consistency.
- Enhanced `GetUserUsableGroups` logic to ensure it returns a copy of the groups, preventing unintended modifications.

controller/user.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"one-api/common"
 	"one-api/model"
+	"one-api/setting"
 	"strconv"
 	"strings"
 	"sync"
@@ -454,7 +455,11 @@ func GetUserModels(c *gin.Context) {
 		})
 		return
 	}
-	models := model.GetGroupModels(user.Group)
+	groups := setting.GetUserUsableGroups(user.Group)
+	var models []string
+	for group := range groups {
+		models = append(models, model.GetGroupModels(group)...)
+	}
 	c.JSON(http.StatusOK, gin.H{
 		"success": true,
 		"message": "",