Validate .pyi is self consistent with our bindings

[jleibs]

We currently need to maintain a .pyi file that matches the signatures of our bindings.

It's very easy to accidentally mess this up, especially when things are being renamed.

See, for example:

• Rename TimeColumn -> IndexColumn and assorted fixes #7636
• Fix pyi signature for IndexColumnSelector #7644

Eventually PyO3 should support .pyi generation (PyO3/pyo3#2454), however for the time being we need some kind of system to keep us from messing this up.