Move all API results with basic AsyncGenerator to its own object for feature parity with other API results

Currently, all API calls that only return a generic AsyncGenerator do not expose the currently used pagination cursor or have access to the to_dict() function that every single other API result has.

To establish feature parity, rework the `Twitch._build_generator()` function to use a custom object which does the work of the current generator and also implements the missing features. 