Use mro lookup for class constants

[fleetingbytes]

General regex could have class constant properties lookup in MRO whether they shall return str or bytes. No building blocks would be necessary for Sre and Bre. They would probably become one and the same class?

[fleetingbytes]

Sre and Bre will still be distinct because they they will have str vs bytes as one of their mixin classes

[fleetingbytes]

Maybe use functools.cached_property instead of the normal property decorator for these class constants.