NMS support for Minecraft 26.2

[kalkafox]

I took your feedback from #405 and ran the model to rework the update around the existing adapter structure instead of adding another full copy of the Paper internals, which makes the most sense.

The common Paper implementation now lives in the 26.2 adapter, and the 26.1 adapter has been reduced to small compatibility for the NMS/API differences that changed between 26.1 and 26.2.

The remaining 26.1 parts cover the older access patterns for loot tables, ender chest contents, placeholder item constants, advancement cleanup, and fallback spawn/world assignment.

Hopefully it's not too messy and easier to work with. I was a bit overzealous in the previous PR and closed it in shame and I squashed the previous commits anyhow. The slot change will probably still need work as you mentioned before. Overall it adds about ~6 KB to the jar. I probably should've looked at that too before doing my initial PR lol. Thank you for maintaining!

[Jikoo]

Awesome, thank you. This is honestly such a huge springboard for doing the update (which I hope to start on tonight). I'll dig out my checklist.

Also, thank you for restoring some of my faith in humanity. I've seen a decent number of AI PRs at this point across various projects, and seeing someone take feedback and do prompting based on that is a breath of fresh air. I feel like most people who submit AI PRs just copy any feedback into their session and hope.
If you don't mind me asking, what tools/model are you using and how do you approach a problem of this nature?

[kalkafox]

I'm using a free trial of Codex with extra high reasoning on GPT 5.5, so nothing too complicated. Honestly, the initial prompt was just "Port this to 26.2" with no additional context. I wasn't paying too much attention to how the NMS structure is supposed to look like at first.

After closing the previous PR I gave the session the details of it regarding the adapters, which refactored the paper26_1 adapter to be a thin compatibility layer over paper26_2 which is where the shared core now sits. Hope it helps! I haven't run into any issues on our 26.2 test server so far with most of the container functionality, I'll report back if I do.