Ratelimiting Support

[shockpast]

It would be awesome to respect ratelimits of osu! beatmap mirrors, and manually slow down downloader, to avoid getting temporarily banned.

[shockpast]

ratelimits:

• catboy.best: 120/min, 2500/daily (download route)
• osu.direct: ~40/min, or 1 map each second if they are not cached (download route)
• beatconnect.io: unknown
• sayobot.cn: unknown
• nerinyan.moe: unknown

[shockpast]

Partially added feat(mirrors)!: added ratelimiter (hopefully less bans), still experimental, since most of the limits are not known to me.