Redesign test suite

[leonlan]

I have been sloppy in writing my tests. Especially with the module rehaul, most of the tests are not in the right place, or not even implemented at all. I think that coverage can be very helpful to detect the missing spots.

TODOs

• Add coverage
• Implement tests for parse module
• Gather all the VRPLIB instances that you can find
  • ORTEC Euro-NeurIPS VRPTW instances