Add versioning concept for repo sync db files and pkgbase output files

This fixes #42 (closed) by implementing

• versioned pydantic models
• a set of expandable expectations when parsing input (via repo sync db files or pkgbase JSON files)
• move models to a module, that can expose top-level functionality more easily

Additionally this fixes the .coverage file location to be top-level again (where tools use it) and isort to not automatically sort when it should only check the status.

All type error ignores are made specific by configuring mypy accordingly.