Merge 1-10K mods into a single "Key Count" mod

[cl8n]

another attempt at #25505, closes #25252

069053b is my attempt to convert the previous mod acronyms into something useful, but I'm not sure if this is the right way to go about it. and I have not tested this with the full web stack yet but I suspect things will break there...

I am also not confident that my changes to DifficultyAdjustmentMods for the diff calculator are correct, because I haven't checked to see how those are used in other projects yet

[bdach]

I'll just say that this merging of key mods has infrastructural concerns that will need handling in server side components and probably also web. Thus, I am personally not reviewing it this year as I consider it largely unimportant in the scale of everything.

[cl8n]

👌 no rush. I'll take a look into the server implications myself in the meantime, I'm just not confident I will be able to propose a good fix there if it gets complicated

[bdach]

For starters:

• https://github.com/ppy/osu-queue-score-statistics/blob/b58b50598db10081b1e27579e194bb9262001837/osu.Server.Queues.ScoreStatisticsProcessor/Processors/ScorePerformanceProcessor.cs#L160-L166
• osu-difficulty-calculator should actually just work
• web display (key mods have separate leaderboards per key, so there's the whole smorgasbord of what's going to happen to indexing, to display, etc etc) - this is probably the single biggest issue here