RFC
Until now, if the initial `BeginPlaySession()` call failed, the client
would continue operating as if it didn't - it would still continue to
send frames and call `EndPlaySession()` at the end of a session.
Server-side, two things generally can happen after this:
- The sent frames and the `EndPlaySession()` call are
[completely](https://github.com/ppy/osu-server-spectator/blob/7bab117e9d161455485368f63a0607a9e53f9f8a/osu.Server.Spectator/Hubs/Spectator/SpectatorHub.cs#L122-L125)
[ignored](https://github.com/ppy/osu-server-spectator/blob/7bab117e9d161455485368f63a0607a9e53f9f8a/osu.Server.Spectator/Hubs/Spectator/SpectatorHub.cs#L153-L157)
as no-ops, or
- A hub filter (like `ClientVersionChecker`) that failed the initial
`BeginPlaySession()` call continues to fail the calls to
`SendFrameData()` and `EndPlaySession()`, all the while creating a storm
in logs, because it needs to throw `HubException`s to communicate to
users that they need to update their game, and the exceptions can't be
silenced from logs because they look like every other failure.
To that end, this has two goals: reduce useless network traffic, and
reduce noise in spectator server logs after the client version checks
were recently reactivated.
Probably needs tests, but unsure if everyone's going to be on board with
this to begin with to be quite frank, so I'm leaving tests for when I'm
told this needs tests.
When the server requests a disconnect due to a user connecting
via a second device, the client will now log the user out on the first
device and show a notification informing them of the cause of
disconnection.
There was a lot of weirdness here, such as storing the playing users,
clearing the playing users from test scenes (!!), and storing the users
being wathed.
This was all a thing because the previous implementation overrode the
base method implementations, which is no longer a thing.