fix check_deps.py crash on Python < 3.10

str | None union syntax requires Python 3.10+. Adding
from __future__ import annotations makes all annotations
lazy so the script can run on older Python and report the
version requirement instead of crashing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

check_deps.py

@@ -6,6 +6,8 @@ Usage:
     python check_deps.py
 """
 
+from __future__ import annotations  # allows str | None syntax on Python < 3.10
+
 import importlib.metadata
 import sys