adding interfaces for type hints

[akmazian]

hiii Scott,

Before I start I just wanna say thank you so much for creating this package :) It has truly been super helpful since our lab only has one set of FACSdiva (yikes). Anyways, here's a quick PR that added .pyi files for type hints 💡

If you don't mind taking a look at those and lemme know if anything feels off!

Best, AZ Zhang Ünal-Brar Labs UC Berkeley