[Enhance] [Refactor] Add API about characters

- Add API endpoints about characters
- Some small changes in refactoring

latest version/server/purchase.py

@@ -1,12 +1,13 @@
 from time import time
 
+from flask import Blueprint, request
+
 from core.error import InputError, ItemUnavailable, PostError
 from core.item import ItemFactory, Stamina6
 from core.purchase import Purchase, PurchaseList
 from core.redeem import UserRedeem
 from core.sql import Connect
 from core.user import UserOnline
-from flask import Blueprint, request
 
 from .auth import auth_required
 from .func import arc_try, success_return