Litemapy

* Massively improve saving performance by using Numpy to count non-air blocks (by llGaetanll).
* Obsolete region palette entries are now pruned.
* `BlockState` is now hashable.
* Region palettes are now exposed as read-only properties.

* Breaking change: the `BlockState` constructor no longer takes properties as a single `properties` argument.
Each property must be supplied as its own keyword argument instead.
E.g. `BlockState("minecraft:acacia_log", facing="west")`
* Added `BlockState.with_properties()` and `BlockState.with_blockid()` to create copies of block states
but with different ids and properties.
* Added `Region.filter()` to allow for efficient block replacement.
* Schematic palettes are now always optimized before saving

* Method to convert regions to the sponge schematic NBT format
* Fix crash with litematics created by newer versions of Litematica "id -> The required key is missing in the (Tile)Entity's NBT Compound",
It was caused by Litematica no longer specifying a TileEntity's ID in its own NBT structure
(it can be assumed by looking the block at the TileEntity's coordinates)
* Made internal list fields access only (Regionentities, Regiontile_entities, Regionblock_ticks, Regionfluid_ticks)

* Method to convert regions to the vanilla Minecraft structure NBT format

* Basic support for entities
* Basic support for tile entities
* Basic support for preview images
* Retain block and fluid pending ticks when reading and then saving a litematic

* Uses nbtlib versions above 2.0.3, older 2.0.X versions are broken.