Initial port to 1.18.2

This release is the initial release of MCPaint for 1.18.2.

It brings several improvements over the 1.17 version:

Changelog:

- Initial port to 1.18.2 (by Nyfaria)

- Improved optimizer performance (should result in fewer/shorter lag spikes when loading a world with many painting)

- Reduced disk space and network bandwith (if multiplayer) utilization by using a paletted saving approach