Biome-independent structure tables

[BoySanic]

Fixes #1805
Implements biome-independent structure tables.

The way these work:

Structure tables are loaded into the game along with all other assets.
When loading biomes, each biome checks its biomeTags (new feature, currently unused) against the biomeTags in each structure table that was loaded previously. If any biomeTags match, add the structures from those tables into the biome's internal structure table in memory at world load time.

Additionally, if a structure table has an empty .biomeTags (len == 0), it should spawn those structures in all biomes. So those structures are added to all biomes' internal structure table.

Implementation details:

Moved hashing functions out of src/server/terrain/biomes.zig into src/utils/hash.zig
Moved SimpleStructureModel into src/server/terrain/structures.zig from src/server/terrain/biomes.zig.

Example structure table .zig.zon in assets/cubyz/structure_tables in this branch.

[codemob-dev]

Instead of adding a new asset type, why not just add the structures directly to the biomes when loading the structure table?

[BoySanic]

I guess that could work.

[BoySanic]

I'm investigating this a little and it might be easiest to use the approach I took with a new asset type.

At least this way we can have assets load in the structure tables and have a place to put them.
Otherwise, I'm not sure how you'd load structure tables without adding another way to load assets that isn't the standard flow in assets.zig, which may not be preferable due to diverging ways to load assets.

[codemob-dev]

Why not just put this directly into utils.zig? It's small enough that it doesn't need its own file.

[codemob-dev]

Moving this to a new file should probably be in a separate PR, it make the diff hard to read.

[BoySanic]

I have a single commit for this that I can cherrypick and PR separately before we tackle this one.

If that's preferred I can split that out and PR it on its own to simplify this PR (for when it's no longer a draft)

[codemob-dev]

Yeah, definitely. Quantum doesn't like multiple less related changes in one PR (I don't either)

[BoySanic]

On the topic of this PR, I was thinking about how addons might target biomes and with the current approach they'd use biome tags.

I think it may make sense to allow the structure table to use the biome's id as a tag, too. Just check if the structure table's biomeTags contains the biome's Id (it would just be an or on the current check that is used) and it'd make that easier. Then we don't have to come up with tags to target specific biomes, we just use their id as a tag logically.

In the future I envision we start categorizing biomes. like cubyz:cold, cubyz:humid, cubyz:dry, cubyz:hot, and so on for the various "tags" that could apply to a biome. Then, similar to the #1805 example, maybe an addon that adds igloos would create a structure table containing that igloo and it would set its biomeTags to cubyz:cold or something, so the igloos are added to biomes that are tagged cubyz:cold.