Note functools.cache for the future.

On Python 3.9+, the `functools.cache` decorator [^1] has the same effect as
`functools.lru_cache(maxsize=None)`, but is easier to write and has a name that
exposes fewer of its implementation details.

[^1]: https://docs.python.org/3/library/functools.html#functools.cache

refresh.template.py

@@ -20,7 +20,7 @@
 
 import concurrent.futures
 import enum
-import functools
+import functools # MIN_PY=3.9: Replace `functools.lru_cache(maxsize=None)` with `functools.cache`.
 import itertools
 import json
 import locale