Probably closes https://github.com/ppy/osu/issues/34645.
Obviously this is only good if the score has managed to process online
and slot into a leaderboard before the user requested a retry. I can't
make miracles happen.
Notably this is not applied to quick retry, because it would make quick
retry slower, and the presumption is that if the user is quick-retrying
their last score is likely useless for global leaderboards anyway. (The
one exception to that last part is possibly quick-retrying from results
screen, which is a flow that we have, but maybe fine to ignore it...?)
This seems like the lowest friction way of fixing
https://github.com/ppy/osu/issues/30885.
We could also only null this on application, but this feels worse
because
- It would require local handling (potentially complex) in
`BeatmapOffsetControl` if we want to continue displaying the graph and
button after clicking it.
- It would make the session static very specific in usage and
potentially make future usage not possible due to being nulled in only
a very specific scenario.
One might argue that it would be nice to have this non-null until the
next play, but if such a usage comes up I'd propose we rename this
session static and add a new one with that purpose.