Following discussions on discord, this seems like the most agreed upon
value. Increasing this is important so that imported legacy scores don't
lose too much value.
Doesn't do much for the client; mostly a safety for osu-web's sake,
as without the change it could theoretically fail to validate the mod
properly in multiplayer contexts.
In discussion with nanaya, we likely want this now that we're adding the
ability for some icons to be extended. Historically mod icons have been
displayed in a stable but arbitrary order (based on their position in
the `Mods` enum).
This change aims to make them stable across lazer scores (where they are
stored based on .. the order the user selected them).