Cave-in Fix

<span style="color: #d35400;">Thanks to RossTheGreat for providing his cave-in patches from InterestingOreGen. This mod is compatible with IOG, but it also works without that mod installed.</span>

This mod fixes certain balance problems with the (currently half-baked and unfinished) optional cave-ins mechanic in vintage story.

CORE FEATURES:
- Unstable blocks (IE: rock, cracked rock, ore) will cap their instability at the stability of the block below them. This means, if a more unstable block is above a more stable rock, there won't be cave-ins caused by blocks the player cannot see (assuming the stable block is the visible ceiling).
- During world generation, naturally generated caves and overhangs will generate a layer of "hardened rock" that prevents caves and overhangs from being inherently unstable, especially caves in sedimentary rock. If you've ever played terrafirmacraft 1.20+, this is pretty much the same mechanic as is implemented there.

- Includes a config option to globally modify the instability of collapsible blocks. InstabilityMultiplier: 0.5 will decrease all instability by half, etc.

FEATURES FROM IOG CODE:
- Removes cave-ins caused by block placement - only breaking blocks will cause a cave-in.
- Smart IOG cave-in logic that creates ellipsoid collapses centered at an exposed ceiling block, replacing the vanilla cave-in logic.
- Cave-ins now only occur when stone blocks are are 100 percent instability and exposed to the air, instead of technically having a chance to collapse at all levels of instability above zero.

The intent of this mod is for the majority of cave-ins to be caused by player mining activity, not worldgen. This should eliminate certain frustrations with the unfinished vanilla cave-in system for those who choose to use it.