Cave Overhaul

warning: new chunks WILL have different cave gen and it WILL make your world look kinda weird

Commit 3c84e69

• Fixed an issue where noise caves could end abruptly in tall vertical walls instead of tapering off naturally.
• Slightly more noise caves generate in areas that previously had none.

Commit 7eb304c

• Fixed an issue where caves from the old-world carver could terminate in flat stone walls aligned to chunk boundaries.
• Cave shape and density in old-world carver regions will shift slightly as a side effect — tunnels now cluster a bit more tightly within their home area.

Commit 6d50344

• Fixed an issue where all cave layers shared a single structural noise pattern, causing layers (especially the duplicated ones below y=-64) to look the same as each other.
• Each cave layer now generates with its own independent structural shape for more variety between depths.

Commit 385c50a

• Unified how caves and underground rivers apply their large-scale terrain warping, so they pull from a single consistent pattern instead of independent ones.
• As a result, noise caves WILL generate differently from previous versions, especially at greater depths. Existing worlds will show a visible seam between old and newly-generated chunks.