Proguard rules don't keep constructor data classes

[shekibobo]

The proguard rules keep constructor.io package data models instead of io.constructor package data models. I'm not sure why they didn't cause problems with older versions of AGP/R8, but between 7.0.0-beta03 and 7.0.0-beta05 the proguard rules in the library are not sufficient to keep those data classes from being removed or obfuscated.