Synchronize Python versions across local dev, CI, and prod

[duck-master]

I'm using Python 3.11.1 locally; CI is using Python 3.7.x; and production (I believe) is using 3.12.11. This has the potential to cause serious errors. For example, GitHub Actions choked on my PR for two different reasons; one being that mypy 1.17 isn't available for a python version this old, and another being that you can't subscript into the type dict or list in Python <3.9 when making a type definition. Also, our requirements.txt specifies tomli, which is now deprecated. We should decide on a single Python version to use and ensure that we all have this installed locally as well as using it in both CI and prod.