This eliminates the possibility of having `request.user` as
`RemoteZulipServer` by refactoring it as an attribute of `RequestNotes`.
So we can effectively narrow the type of `request.user` by testing
`user.is_authenticated` in most cases (except that of `SCIMClient`) in
code paths that require access to `.format_requestor_for_logs` where we
previously expect either `UserProfile` or `RemoteZulipServer` backed by
the implied polymorphism.
Signed-off-by: Zixuan James Li <p359101898@gmail.com>
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