_FixedOffset Base Class

[AlecRosenbaum]

While most timezone classes share a BaseTzInfo class, _FixedOffset does not. Functionally it doesn't really make a difference, but with stricter type checking it can become troublesome. Some interfaces from third-party projects specify BaseTzInfo within type annotations where _FixedOffset should also work.

Would you be open to a change that just replaces class _FixedOffset(datetime.tzinfo): with class _FixedOffset(BaseTzInfo):?