Helpers in ActionCable::ChannelStub

Do we really need those shorten test methods?

      def confirmed?

      def rejected?

I used rejected? in channel#unsubscribed, tests passed well. But in review apps this shorter method was missing.

I consider this a bug. Removing this aliases would introduce breaking changes, so, it could be only done in Rails 7. Instead, we can replace ChannelStub with delegation or smth like that to avoid leaking test methods to the application code. Or we can add aliases to Channel::Base (but that could be a potential breaking change as well, though not that big).