Use sqlalchemy v2 style API

[chrisjsewell]

Now supported with 1.4, see https://docs.sqlalchemy.org/en/14/changelog/migration_14.html#orm-query-is-internally-unified-with-select-update-delete-2-0-style-execution-available

I think maybesession.query needs to be changed to select?

[chrisjsewell]

also use WAL mode for connections, which improves concurrency: https://sqlite.org/wal.html
See e.g. https://github.com/aiidateam/disk-objectstore/blob/65a3e5d9b8c95d7f9a7309a01f8be68bc11be1bd/disk_objectstore/database.py#L34