KISS – Keep Inventories Sorted, Simple

• Support for Minecraft 1.21.2 and 1.21.3

Let me know if there's any issues. I tested it and things seemed fine, but this is the first time for me updating a mod with significant changes to Minecraft under the hood. I won't be updating my own main world/server to 1.21.2 right away, so there might be problems I wouldn't notice myself.