Implement build/publish actions in ci

Rename represent to attrs_as_tuples

also add flat arg to it, inspired by values_list of Django's QuerySet.

Merge tests and pre-commit in one workflow

Bump version 0.5.0 and update changelog

Fix pylance type errors

also remove class attrs of Registerer.
bump patch version.

Bump version 0.4.2

Update register to be more language-server friendly

No API changes. Also patch release.

Bump version 0.4.0

Bump version 0.3.1

Release v0.3.0