fix Python 3.9 compatibility (str | None union syntax)

parser.py and update_mods.py were missing
'from __future__ import annotations', causing a TypeError on
Python < 3.10 when the X | Y union syntax is evaluated at runtime.
All other modules already had the import.

Also lowers MIN_PYTHON from 3.11 to 3.9 -- the toolchain does not
use any Python 3.10/3.11-specific stdlib features beyond the union
annotation syntax which is now handled by the future import.

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

arma_modlist_tools/parser.py

@@ -15,6 +15,8 @@ Typical usage::
     presets = parse_modlist_dir("modlist_html")
 """
 
+from __future__ import annotations
+
 import re
 import xml.etree.ElementTree as ET
 from pathlib import Path