fix: add missing __future__ import to validation.py for Python 3.9

Author: tom-sapletta-com

pyqual/validation.py

@@ -22,6 +22,8 @@
 (PROJECT) or surface it to the user (PIPELINE/LLM).
 """
 
+from __future__ import annotations
+
 import re
 import shutil
 from dataclasses import dataclass, field