Sable Sub-level Loading System Fix

Changes how Sable determines when and how sublevels are loaded and unloaded.

Prevents sub-levels from unloading when the only player loading them is dead, fixes Sable's sub-level loading and unloading when a player is on a sub-level but its holding chunk is unloaded, and keeps sub-levels loaded when any chunk within the player-requested view distance contains any part of that sub-level (even if no player is standing on it).

Useful for modpacks/instances in which you intend to create very large sub-levels that span many chunks.

Also, you can ignore the credit the license wants you to give me if you add this to the modpack from Modrinth's explore content, since it will then appear in the modpack's mod list.

Requires Sable 2.0.3 or newer.