Fix Python 3.11 compatibility: add future annotations import

Add `from __future__ import annotations` to fix type hint syntax
error in Python 3.11 where list[str] is not subscriptable in function
signatures without this import.

Fixes CI test failures in PR #36.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: ngjunsiang

campus_python/auth/v1/clients.py

@@ -2,6 +2,7 @@
 
 Campus Auth Clients resource (v1).
 """
+from __future__ import annotations
 
 import campus.model