It is not possible to produce type annotations that work with both
versions 1.4 and 2.0. So keep to the principle of only supporting
newest versions when it comes to mypy. This means that some types
may have to be string quoted to not cause issues when running with
SQLAlchemy 1.4.
Also defines an extended connection object that includes access to
the table definitions. Makes it easier to access the tables from
code that has been split off into separate modules.
