feat: multi-phase module initialization, heap based types (#307)

See:
- [PEP 384](https://peps.python.org/pep-0384/)
- [PEP 489](https://peps.python.org/pep-0489/)
- [PEP 573](https://peps.python.org/pep-0573/)
- [Isolating Extensions How-To](https://docs.python.org/3/howto/isolating-extensions.html)

Co-authored-by: David Glick <david@glicksoftware.com>

Author: tseaver