typing.Annotated
https://docs.python.org/ja/3/library/typing.html#typing.Annotated
Python 3.9から
Annotated[<type>, <metadata>]
例:
T1 = Annotated[int, ValueRange(-10, 5)]
ValueRangeは標準ライブラリのdataclassとして定義
PEP 593 – Flexible function and variable annotations