code-to10 v6 A14 batch2: test E402/F401 cleanup plus touched-file residual E,F cleanup

(cherry picked from commit 1db02545f74c96b3b92be4fc32954659cec1f814)

Reconcile-conflict: A14b E402 imports referencing cloud.handler_core (does not exist here; core methods live in server.py) — kept HEAD imports with incoming's noqa: E402 markers, dropped the unused core_mod import (verified unused elsewhere in both files).

cloud/tests/test_longfunc_remaining.py

@@ -13,7 +13,6 @@
 套件覆盖，本文件不重复测路由，只测抽出子块本身。
 """
 
-import os
 import sys
 import unittest
 from pathlib import Path