fix: refactor code so most things work without sqlalchemy

also refactor tests to help ensure that remains true

Move tests out of the installed package set

this seems to be better practice. from what i can tell this is a
clean move with no breakage.. and built package files no longer seem
to include test modules

Make 'tests' a proper subpackage again; add some tests

Trying to make more of an effort here...

Add `User.get_email_address()` and `User.email_address`.

For now, these will do. Probably need to revisit that at some point.