Stator code reload

[Jamie Bliss]

Add an option to the stator runner to automatically reload on code change.

This should help improve developer experience and tighten feedback loops.

[Henri Dickson]

good idea. the alternative I do right now is mount the dev code folder in container and restart container to reload.

[Andrew Godwin]

I'm going to explore moving Stator out to be an actual separate package soon, so this might make sense to do then.