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

Author: tom-sapletta-com

pyqual/llm.py

@@ -5,6 +5,8 @@
 provided so that pyqual keeps working on Python 3.9 or without ``llx``.
 """
 
+from __future__ import annotations
+
 try:
     # Prefer the upstream canonical implementation.
     from llx.llm import (  # noqa: F401