Previously, when unmuting a user, we used to make
two database fetches - one to verify that the user
is has been muted before, and one while actually
unmuting the user.
This reduces that to one, by passing around the
`MutedUser` object fetched in the first round.
Since the new function returns `Optional[MutedUser]`,
we need to use a hack for events tests, because
mypy does not yet use the type inferred from
`assert foo is not None` in nested functions like lambdas.
See python/mypy@8780d45507.
Instead of using internal functions for data setup,
we use the API so that these tests are more
end-to-end.
This commit also removes a now unnecessary
`if date_muted is None` check.
Adds backend code for the mute users feature.
This is just infrastructure work (database
interactions, helpers, tests, events, API docs
etc) and does not involve any behavioral/semantic
aspects of muted users.
Adds POST and DELETE endpoints, to keep the
URL scheme mostly consistent in terms of `users/me`.
TODOs:
1. Add tests for exporting `zulip_muteduser` database table.
2. Add dedicated methods to python-zulip-api to be used
in place of the current `client.call_endpoint` implementation.