Allow un-sequenced executions of paywall functions

I’ve noticed that if some functions of paywall are called at the same time, they don’t work.
Example: call getTrialInfo and getUser without awaiting the calls. As a result, the functions won’t be properly executed.

This is important because the paywall functions can be used for checking the state and showing some parts of the UI based on the result. E.g. I want to call getTrialInfo to show or hide the “Restore Account” button, but if at the same time openPaywall will be called, the first function will fail. So, for this to work properly I have to create some kind of a queue where the calls are totally flat.