core: migrate code to benefit from 3.9 stuff (#401)

for now keeping ruff on 3.8 target version, need to sort out modules as well

my/core/tests/auto_stats.py

@@ -2,11 +2,11 @@
 Helper 'module' for test_guess_stats
 """
 
+from collections.abc import Iterable, Iterator, Sequence
 from contextlib import contextmanager
 from dataclasses import dataclass
 from datetime import datetime, timedelta
 from pathlib import Path
-from typing import Iterable, Iterator, Sequence
 
 
 @dataclass