Making updates of the cache as an exported function

[Melkiades]

There are few cravats for this being a vignette:

• (unless specified by a dedicated flag) building vignettes is part of R CMD BUILD and build step is part of installing from sources, e.g. installing from GH. I am a little afraid of installation performance here.
• Vignettes are exposed to the users. Do we really expect that users will read it?
  Having said that, I don't think that vignette is a good idea. Please correct me if I am missing something.
  To me, data files are integral part of the package. Script Functionality that creates them should be considered as an utility.
  Alternative way would be to introduce something like refresh() / snapshot() / create_new_datasets() function in the package namespace but do we really expect package users to trigger this procedure? I feel it's more on package maintainers. Moreover, this could make it a little bit more difficult to keep test coverage high - you would have to do the mocking or other clever tricks to be able to test that.

Originally posted by @pawelru in #290 (comment)

I would keep the vignette with eval = FALSE so to keep some connection with the past (and keep some guidance for updating the cache, which is good for a vignette). For tests and examples, we will see. I think anyway, if there are no updates on the diff with origin/main it should not do anything, so tests should go fine, but we need to be sure for branches etc..