Load and solve VRP instances

[AntoinePrv]

Discussed in https://github.com/ds4dm/ecole/discussions/287

^{Originally posted by ndrwnaguib November 23, 2021} Hi,

I am trying to load CVRPLIB into Ecole. However, I do not think designing it as an instance generator is the way. I view it as a loader instead. I'm not sure what steps I should follow to achieve that, I'd appreciate any pointers.

Off topic: if you believe there would be considerable use for these datasets, I also would like to contribute it to Ecole problem instances.

Thank you.

Need to investigate how to load and solve VRP files. A question I have is whether the problem in the example is fully represented in the SCIP model, or if it has implicit variables (the custom pricer).