this reduces the footprint of RuntimeBlockMapping by a further 1 MB, as well as simplifying various parts of the code, and solidifying the immutability guarantee of BlockStateData.
this commit provides a central place where all block data can go to be upgraded to the latest version (currently 1.19), irrespective of how old it is.
Previously I had issues during debugging, because it wasn't possible to just upgrade a block without deserializing it into a Block object, which isn't currently supported for many blocks.
This commit solves that problem by separating the upgrading from the deserialization.
a non-generated chunk is now always represented by NULL. This forces the case of ungenerated chunks to be handled by all code, which is necessary because ungenerated chunks cannot be interacted with or modified in any meaningful way.
