fast generate option?

[will]

Is there, or would you consider adding, a way to only generate RBIs for gems that have changed?

Some of the gems I have to use take a long time to require in general, and also a while to generate rbi for, so it'd be nice to skip that work if possible. I understand the need to go through everything if requires change though, so maybe if this was an extra flag to generate rather than the default.