Format, restructure and invalidiations

[oameye]

The PR does many things:

• I added a formatter CI, which formats all files to have a uniform stye. If someone makes a PR, It will format the branch to a unified chose style. Atm I went for JuliaDiff/BlueStyle: A Julia style guide that lives in a blue world (github.com).
• I checked that there are now implicit imports with ExplicitImports.jl. This makes sure that there are no name clashes and every code that is used from a dependency is explicitly stated. This makes our lives also easier when debugging code. I added these checks also to the test suite.
• I tested the package with JuliaTesting/Aqua.jl: Auto QUality Assurance for Julia packages (github.com). The packages check if the quality of the code is up to standards, i.e., no method-ambiguities (see example), no stale dependencies, all dependencies have compat entry, no type-piracy, etc ... Again, these test are also added to the test suite.
• I also did some quick checks with JET.jl. This package is the most exciting. It hunt for type-instabilities. This increase the performance of the code by making it easier for the compiler to compile the function methods. Type instabilities is the largest reason that our time-to-first-execution is so large when computing the equations. I have hunted down a couple, but we still need to do more.
• I added a bit more test, although we need much more in general. I think only 40% of the code is covered in the tests.

https://github.com/aviatesk/JET.jl
https://github.com/ericphanson/ExplicitImports.jl
https://github.com/domluna/JuliaFormatter.jl
https://github.com/MilesCranmer/DispatchDoctor.jl
https://github.com/JuliaTesting/Aqua.jl