Automate testing and updating of stub files in Python bindings

[paleolimbot]

Apparently stubtest is not quite sufficient to detect out-of-date stubs, as found in #606, and generating the stubs using mypy on CI and checking that the .pyi files didn't change also didn't quite work out-of-the-box. There are some options for generating type stubs that might be simpler than mypy or might not require installing in advance, and it might be necessary to not use .pyi files that start with an underscore for this to work with mypy.

In general, we should be able to follow the work in pyarrow to provide stubs that can at least enable a useful developer experience and user experience for the few object types that we don't provide Python wrappers for (e.g., buffer view).