Upgrade to sqlalchemy 2

[mhauru]

Upgrading from 1.4 to 2 is currently held back by sqlacodegen not supporting 2. There is a PR, but it hasn't made progress for a while, due to the maintainer having competing priorities: agronholm/sqlacodegen#249

We should do this once we can though. It would enable

• moving to smartnoise-sql 1.0 (we are on 0.2)
• using some more developed asyncio stuff in sqlalchemy
• type hints for sqlalchemy

[mhauru]

The upgrade to SQLAlchemy 2 is in sqlacodegen/main, but there's no release yet with that work included. The maintainer says he'll make one soon. Once that is done, the whole upgrade path to using SQLAlchemy 2 and the latest snsql version opens up for us, see the opening message. I started work on doing this on the branch sqlalchemy2 if anyone wants to get to it while I'm gone.

[mhauru]

Done