use code annotations for style etc

[lsf37]

Mostly putting this here so someone can pick it up if they feel like implementing it:

It could be nice to have the style checker directly comment on the code instead of outputting a diff (see also theory-linter, which does that)

Main blocker for that is that code annotations for GitHub actions only work for PRs from within the repo, not for forks, which is the common case. You can implement comments/code annotations from a GitHub app, though. This would have to be written and hosted somewhere. That is all solvable, but needs someone with a bit of time and web app knowledge.

[lsf37]

Could potentially use the a separate workflow for the annotations, using a workflow_run tigger