Formatting

[carstenbauer]

Let's ensure "proper" formatting according to the SciML style (on the main branch). I've set up a GitHub action that checks proper formatting for all pushes to main.

How to format?

• Use https://github.com/domluna/JuliaFormatter.jl manually (using JuliaFormatter; format(".")), or
• Use the formatting features of VSCode, specifically the Julia Extension.

(cc @Mellich)