Up until now, the `UserActivity` class hierarchy contained things like
beatmap info, room info, full replay info, etc. While this was
convenient, it is soon going to be less so, as the data is sent over the
wire to the spectator server so that the user's activity can be
broadcast to other clients.
To counteract this without creating a second separate and slimmed-down
class hierarchy, slim down the `UserActivity` structure to contain the
bare minimum amounts of data such that the structures aren't overly
large and complex to serialise, but also contain enough data that they
can be used by receiving clients directly without having to do beatmap
or score lookups.
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.
Mostly places that can interact with imported replays.
There are other places that use the online ID as a sort tiebreaker, or
to check presence of a score on results screens, but they should
probably still continue to only use `OnlineID`, since all scores with a
legacy online ID should have an online ID, but the converse is not
generally true.
This time for `SocketException`s. I seem to recall looking at this and
deciding there was a reason to not catch socket exceptions, but on
revisiting it seems sane to do so.
This covers a fail case like reported:
```
2023-10-06 03:24:17 [verbose]: Request to https://lazer.ppy.sh/oauth/token failed with System.Net.Http.HttpRequestException: No such host is known. (lazer.ppy.sh:443)
2023-10-06 03:24:17 [verbose]: ---> System.Net.Sockets.SocketException (11001): No such host is known.
2023-10-06 03:24:17 [verbose]: at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
```
Closes https://github.com/ppy/osu/issues/24890 (again).
