fix(dialyxir): Add missing typespecs

[mrapacz]

Type

Fix

Current behaviour

As for now we had to create the dialyxir.ignore_warnings file. We were getting so many because we did not define the UserSocket type (or we actually defined it as
@type t :: %Phoenix.Socket{}, which is not enough (we keep more data inside than the traditional socket). This is why all of the functions dealing with UserSocket are throwing errors.

Expected behaviour

No errors on output.

Motivation / use case

Dialyxir is right about throwing errors here because the type specs and the reality indeed are different.