refactor(group): update user group handling to utilize userUsableGroups directly and add GetUserGroupRatio function

middleware/distributor.go

@@ -94,6 +94,7 @@ func Distribute() func(c *gin.Context) {
 							return
 						}
 						usingGroup = playgroundRequest.Group
+						common.SetContextKey(c, constant.ContextKeyUsingGroup, usingGroup)
 					}
 				}
 				channel, selectGroup, err = service.CacheGetRandomSatisfiedChannel(c, usingGroup, modelRequest.Model, 0)