Introduce a User object
I'm sick of passing around more and more things as tuple items around
the whole world, and needing to edit every call site every time there is
more information about a user. So pass them around together as an
object.
This object has incredibly poorly named fields because we have a
convention that `user` indicates a UserID object, and `user_id`
indicates a string. I tried to clean up the whole repo to fix this, but
gave up. So instead, I introduce a second convention. A user_object is a
User, and a user_id_object is a UserId. I may have cried a little bit.
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