Optimize initialize user code path for known new users

[texuf]

Description

The initialize user code path in typescript first calls getStream to see if a stream exists, then calls create stream. It does so because it

• handles partially created users (if the user lost connectivity half way through)
• handles any upgrades to the protocol (if we add a new user stream in the future)

However calling getStream on a stream that does not exist is an expensive operation (around 2 seconds)

We would like to do this instead: When we know we are dealing with a new user, always call create stream first. In the case where the stream already exists, catch that error and call get stream instead. This will require some exploration to make sure that the error returned in the partially created user case is properly handled.