The intention here is to make things more testable going forward.
Specifically, to remove the "back-door" entrance into `BeatmapCarousel`
where `BeatmapSets` can be set by tests and bypas/block realm retrieval.
This fell out while investigating why the issue with online IDs
mismatching in the `.osu` could be worked around by importing the map
three times in total when starting from it not being available locally.
Here follows an explanation of why that "helped".
Import 1:
- The beatmap set is imported normally.
- Online metadata population sees the online ID mismatch and resets it
on the problematic beatmap.
Import 2:
- The existing beatmap set is found, but deemed not reusable
because of the single beatmap having its ID reset to -1.
- The existing beatmap set is marked deleted, and all the IDs of
its beatmaps are reset to -1.
- The beatmap set is reimported afresh.
- Online metadata population still sees the online ID mismatch
and resets it on the problematic beatmap.
Note that at this point the first import *is still physically present
in the database* but marked deleted.
Import 3:
- When trying to find the existing beatmap set to see if it can be
reused, *the one pending deletion and with its IDs reset -
- the remnant from import 1 - is returned*.
- Because of this, `validateOnlineIds()` resets online IDs
*on the model representing the current reimport*.
- The beatmap set is reimported yet again.
- With the online ID reset, the online metadata population check for
online ID mismatch does not run because *the IDs were reset to -1*
earlier.
Preferring undeleted models when picking the model instance for reuse
prevents this scenario.
Doing this alleviates https://github.com/ppy/osu/issues/29982, as the
currently online display utilises the user lookup cache, and currently
is hitting rate limits due to the amount of data retrieved from the `GET
/users` endpoint. Switching to `GET /users/lookup` reduces the chance of
this happening.
People keep asking why https://github.com/ppy/osu/pull/29553 didn't fix
their databases (as stated in the PR, it didn't intend to), so this
should do it for them.
