Split recipe code examples into individual files

[tnederlof]

To ease development flow, make CI easier and to reduce the amount of lines in each qmd it could help to separate each of the code examples into individual .r and .py files.

Unfortunately AFAIK there is no way to do this in core Quarto (the built in include only works for .qmd and .md: https://quarto.org/docs/authoring/includes.html#overview). However there is this extension we could use: https://github.com/quarto-ext/include-code-files?tab=readme-ov-file