New dataclass features for old Pythons

An unauthorized continuation of the official dataclasses backport from 3.7 to 3.6, that brings almost every single dataclass feature and optimization from 3.14 to every Python version between 3.6 and 3.13.

Originally created for production usage on RHEL8 systems where the target application is tied hard to system Python.

Intended to also be useful for similar situations on newer LTS editions of Ubuntu, RedHat etc.