November has been a big month for RCS — the mobile messaging protocol championed by Google — and now, the company is capping it off with the announcement of a milestone and some festive new features. First, the number: according to Google, over 1 billion monthly active users are using RCS in Google Messages. That’s huge considering support was scarce just a handful of years ago, though not entirely surprising since it’s been the default messaging service on Android phones for a few…