Add linting to CI and style code

[milanmlft]

• Add config and CI for {lintr}
• Run styler::style_pkg() to style the current code

[stefpiatek]

Ironically this is failing

[milanmlft]

Ironically this is failing

Ugh, it's the r-lib/actions stuff, it was passing with setup-r-dependencies, but that wasn't caching the dependency installation. They told me to use setup-renv but now that's missing a bunch of dependencies 😭