Improve tutorials

[alecandido]

This has been addressed in 30d418d and 940b3c3 to the extent that they are running again ... however, this is not sufficient, since they are by now quite incomprehensible as we have an import complication in game that is never explained. We agree, we want this feature, but the user experience clearly suffers (consider e.g. the theory creation for CT14LLO). Since I don't know what to write I'll leave the pleasure to you @alecandido.

Originally posted by @felixhekhorn in #242 (comment)

Tutorials are for sure relevant, but currently not the main priority.

As discussed with @felixhekhorn, I'd try to improve their quality by improving the underlying code as well, not just adding sugar for users.

If we'll eventually still need some UX improvements, we will consider adding it after internals improvement and stabilization.

[giacomomagni]

Just to mention that related to tutorials we already have #147 #120

[alecandido]

#147 is broader than that (but still blocked by the lack of public API, wip), and #120 instead is strictly related to the technical tool we are using to write them.

[felixhekhorn]

As discussed with Andy Buckley on 4 Oct 2024, at 15:26: we should clarify that for Evolving a PDF all that is needed is an object which exposes an xfxQ2 method