fix: save cart instance before iterating

fix: update Polish translation

fix: upgrade Mezzanine dependency to version 6

fix: update translations

feat: make State/Region fields optional

docs: prepare docs creation on release

chore: upgrade black to 22.3.0

fix: use float for tax rate and format it locally

fix: remove obsolete strip of % from tax_rate and fix type conversion

chore: manage version and changes by semantic-release