* start updating to 1.21.4
* fix block codegen and stop using block data from burger
* rename packet related modules and structs to be simpler
* ItemSlot -> ItemStack for more consistency with mojmap
* .get() -> .into_packet()
* simplify declare_state_packets by removing packet ids
* rename read_from and write_into to azalea_read and azalea_write
* rename McBufReadable and McBufWritable to AzaleaRead and AzaleaWrite
* McBuf -> AzBuf
* remove most uses of into_variant
* update codegen and use resourcelocation names for packets
* implement #[limit(i)] attribute for AzBuf derive macro
* fixes for 1.21.4
* fix examples
* update some physics code and fix ChatType
* remove unused imports in codegen
* re-add some things to migrate.py and update +mc version numbers automatically
* downgrade to 1.21.3 lol
