Previously the beatmap would begin loading at the same time the
`PlayerLoader` class was. This can cause a horribly visible series of
stutters, especially when a storyboard is involved.
Obviously we should be aiming to reduce the stutters via changes to the
beatmap load process (such as incremental storyboard loading,
`DrawableHitObject` pooling, etc.) but this improves user experience
tenfold in the mean time.
If the same ruleset assembly was present more than once in the current
AppDomain, the game would crash. We recently saw this in Rider EAP9.
While this behaviour may change going forward, this is a good safety
measure regardless.