Fixing texture pack stuttering with less ram

[AnyOldName3]

I've said this before, but it might be a good idea to add some level of support for one of the lossless (and maybe some lossy, too) DDS formats in the master branch. Any modern GPU can decode them practically instantly in hardware, and it means we don't need to potentially write out tens of gigabytes for every texture pack. Alternatively, something a bit like Ishiiruka's async shaders might work - we could use the vanilla texture while we wait for the custom one to decode.