Fix the memory leak in the backend

[dysbulic]

What happened?

I'm pretty sure this code is leaking memory and causing the backend process on Render to intermittently die.

It is there because when a user is first connecting there are several near simultaneous calls to useUser that trigger the creation of several users with the same information. All but the first of these will fail because of a uniqueness constraint on the Ethereum address. This code polls to see if a user is currently being created & sleeps if that is going on.

This logic could be replaced with Promises. After a Promise returns, all subsequent awaits of that Promise will return the resolved value directly.

What did you expect to happen?

Not to be getting daily messages that the backend has died.

How can we reproduce the problem (as minimally as possible)?

Monitor sage@metagame.wtf's email and note the messages that the backend service has failed.