Python 3.12 compatibility

[timbernat]

Description

Update package code and build config to allow use with Python 3.12+ as Python 3.11 enters end-of-life.

Todos

Notable points that this PR has either accomplished or will accomplish.

• Enable pip install polymerist without dependency conflicts in envirnment with at least Python 3.12
• Update with minimal changes to source, and without breaking examples
• Resolve Support for Python 3.12 #57

Questions

• What are sources of 3.12 incompatibility?
  • In-code (e.g. typehints, which did change)
  • Dependency (e.g. importlib, OpenFF)
  • Other?

Status

• Confirm import across all subpackages
• Verify CI workflow runs w/ 3.12 added to matrix
• Check compat on PyPI (dev) release
• Ready to go

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