Use __future__.annotations so type hints

work with Python < 2.9

src/fediblockhole/__init__.py

@@ -1,6 +1,6 @@
 """A tool for managing federated Mastodon blocklists
 """
-
+from __future__ import annotations
 import argparse
 import toml
 import csv

src/fediblockhole/blocklists.py

@@ -1,5 +1,6 @@
 """Parse various blocklist data formats
 """
+from __future__ import annotations
 import csv
 import json
 from typing import Iterable

src/fediblockhole/const.py

@@ -1,5 +1,6 @@
 """ Constant objects used by FediBlockHole
 """
+from __future__ import annotations
 import enum
 from typing import NamedTuple, Optional, TypedDict
 from dataclasses import dataclass