Add a 3D world texture implementation.

[ThatRedox]

Closes #1607.

2,115 chunks of my Terralith test world with the max heap set to 1 GB.

This is a 3D biome implementation that uses significantly less memory than TRIVIAL_3D. It is similar to WorldTexture2D where it only stores 8 bits per channel and deduplicates textures.

Testing with 1024 chunks of my Terralith test world:

Implementation	Biome Texture Size (bytes)	Loading Time (sec)	Chunks loaded with 512mb heap
World Texture 3D (this)	61,735,768	56.772	942 / 1024
Trivial 3D	7,250,510,208	50.801	31 / 1024
World Texture 2D	345,600	2.898	1024 / 1024
Trivial 2D	28,434,816	2.816	1024 / 1024

Other changes:

• Separated compact and endFinalization for BiomeStructure
• Added dedicated Interner interface (and tests!) for deduplication
• Refactored WorldTexture2D to share code with WorldTexture3D