Keep a radius of cached regions loaded

Probably just like 1 in every direction (so 9 loaded).

Currently they're only loaded on the chunk packer thread when a chunk is loaded that is in an unloaded cache region.

This kind of defeats the purpose of the cached renderer if it only renders loaded regions, and regions are only loaded if the server tells us about a chunk that's inside them.

Not really an issue unless you're standing near a border tho (coords divisible by 512), but still