Add ability to write anvil chunks

[Earthcomputer]

Objective

• Follow on from Place valence and bevy specific stuff in valence_anvil behind feature flags #510 by adding the ability to write and delete chunks in anvil files.

Solution

• Add a write feature to valence_anvil, behind which the region file allocator is hidden (this is a bit more work to keep track of).
• Users can change the compression method and whether to write oversized chunks, in case they want to write anvil files compatible with older versions of Minecraft.
• LruCache::try_get_or_insert_mut is something I have pull requested to lru, we can switch to that once it's merged.