Add python 3.12 testing

[mikemhenry]

see:

Should we also add testing for Python 3.12 in this PR? or later?

Originally posted by @apayne97 in #90 (comment)

[chrisiacovella]

I think we should address this after we have full pydantic 2 support merged in. No sense trying to support 3.12 on the "legacy" version of the code.