Implement fast binary serializer for PalettedBlockArray

[dktapps]

Serializing palettes is one of the slowest parts of FastChunkSerializer, due to getPalette() building an array, and then passing the result into pack(), which has slow format code parsing and also has to validate every element to check that it's actually an integer.

We can bypass this entirely by implementing a native binary encoder for PalettedBlockArray, which would make FastChunkSerializer quite a bit faster.