Formatting rules

[agg23]

While contributing to Millfork I've constantly had to struggle with the nature of formatting the code. It seems that @KarolS has some sort of pattern (import coalescing, spacing, etc), but I did find it to be somewhat inconsistent, and didn't seem to be backed by some sort of tooling.

I naively started using scalafmt for the LSP work, but that results in a different struggle, as I auto format my own new files, but leave the existing files as formatted as before. It would be preferable if there was some standard to follow (and supporting tools to enforce it).