Add command for recalculating mod multipliers

[bdach]

• End goal is Classic mod multiplier needs reconsidering osu#27685.
• Closes Add command for applying mod multiplier changes #245.
• Depends on Populate score without mods during ongoing imports & add command for backpopulation of it on existing scores #268 for code.
• The command from the above pull should additionally be ran before trying this. When trying to run the command added here, all scores should have total_score_without_mods in the json.

[bdach]

I'll look into the test failures, but a thought that has just occurred to me is that this PR might be going too far.

By which I mean we may want to skip recalculating mod multipliers on leaderboards with significance - I'm thinking multiplayer, playlists, and daily challenge. Which is to say, any multiplayer score would be excluded from having its multiplier recalculated (but also would need to become unranked in the process, which also has pp implications).

Thoughts?

[tsunyoku]

@peppy could I ask that this change is looked at some point soon? With the recent creation of https://discord.com/channels/546120878908506119/1373971097434980463 and conversation happening there, I'm at a point where I'm not sure how exactly we're supposed to go ahead publicly if there's no framework to actually facilitate any changes that may arise from polling. Changing at least the classic multiplier is quite high priority in my opinion.