Create new dataset from `Transformations`

[cmutel]

In the Hestia ontology, a Transformation is: "The Transformation of one Product to a new Product in the same Cycle."

This is complicated because transformations can branch (product A goes down one branch, product B down the other), and there can be allocation. Also, the branches can have multiple steps, so in theory one cycle can produce many products, all linked together in an arborescence.

This should be well tested...

[tfardet]

@cmutel do you want the same result as get_cycle_graph but for a transformations or is this about something else?