Rework Lavaland tunnel themes.

[warriorstar-orion]

What Does This PR Do

This PR:

• creates tunnel theme datums corresponding to the existing burrows, deeprock, and classic caves themes.
• uses the rust-g noise generation functions to create thematically appropriate tunnels.
• removes the "No Lava" mapping helper from lavaland.dmm proper, relying solely on area whitelisting to ensure lava placement for the base map.
• refactors some lava ruins, changing their shape and borders to make them fit better with the new procgen.

I tried to port the thematic elements of the cave themes as closely as possible.

Why It's Good For The Game

For players: The new caves look a lot better and more natural than the old algorithm.

For coders: The existing cave generator was tightly integrated into a specific /turf subtype which contained all its behavior, which 1) was unwieldy and overcomplicated as the cave generation grew more complex and 2) was one of the turf types generated during mineral generation, which would cause issues if trying to rework mineral generation in any way.

I believe using the rust functions will also be faster overall, though I didn't do any actual timing tests.

Images of changes

Classic Caves

Blocked Burrows

Deadly Deeprock

Testing

Generating lots and lots of maps.

Checking spawn rates for mobs/flora/megafauna in progress.

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Declaration

• I confirm that I either do not require pre-approval for this PR, or I have obtained such approval and have included a screenshot to demonstrate this below.

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Changelog

🆑
tweak: Lavaland cave tunnels are now a lot more organic and natural looking.
/:cl:

[warriorstar-orion]

CI is failing because of that runtime in river generation (which happens before caves). Should hopefully be fixed with #26606.

[lewcc]

Looks pretty good to me, though I'd like more eyes on it from lavaland-familiar folks.