Stable build infrastructure & other tooling

[pixelcmtd]

Rn I can't even get an alpha working in the Minecraft Launcher. We really need a GitHub Actions build and in general tooling, especially some formatting. I'm already in the middle of fighting with mcp to find out how to properly build.

[pixelcmtd]

Update: Most of the initial ideas (I can build again, we got automatic alphas from Actions and formatting is fine) are working. However, we could still use some testing and somehow dependencies from a package manager.