I just noticed that ptbs telegram.ReplyMarkup is in fact an invention of PTB, i.e. it's not defined by the official API docs. We should consider removing that class or at least making it private.

IISC it's currently only used for

• type hinting - that could easily be replaced by a type alias
• the static method _check_keyboard_type that's used in the inits of or {Reply, Inline}KeyboardMarkup - that could moved e.g. to tg._utils

Personally, I'd be in favor of just removing the class. @harshil21 IIRC you added the _check_keyboard_type method - what do you think?