In general we're doing things correctly so the realm file shouldn't
expand (unless mass deletions are made from it), but this is a nice way
to manually confirm the behaviour.
Sometimes if using realm studio with osu! running, for instance, the
realm file size can blow out of proportion. This will recover from such
cases.
Note that calling `RealmFactory.Compact` itself is not enough, as it
will fail unless all instances of the realm have been closed.
The tests were relying on the `RulesetID` being set to 0 in the example
beatmap, even though the ruleset *instance* was set to ID 5.
This explicitly adds that 0 value to show intent, and also removes the
incorrect specification of 5 (which would cause the convert filter tests
to fail).
Also updates the filter code to use `OnlineID`, which is required in
realm changes.