draft construct_reprex() and construct_session()

[moodymudskipper]

adresses #74

The idea of construct_workspace() is is to produce readable code that rebuilds the session's objects, and probably attach the right packages (because we can and why not).

There are a few intricacies because then we might want to set options and env variables for instance.

construct_reprex() would produce code to reproduce the situation we encounter at a given point in our code.

[moodymudskipper]

construct_reprex() has been implemented differently so this draft is obsolete for this part.

However we have here some work on construct_session() that we might catch up to at some point