Fix: Vroom handles quantities correctly

[senhalil]

Vroom expects all quantities to be positive (delivery quantities are multiplied with -1)
It cannot handle durations begin modified by vehicle (assert added)
It shouldn't silently ignore services (both pickup and delivery amounts are sent to the solver)

[braktar]

Could you add a test with mixed positive and negative quantities ?

[senhalil]

@braktar share me the test you have on your local when you have time and I will add it the PR

[braktar]

Here are the data i used. I didn't implement the asserts

    problem = VRP.basic
    problem[:units] << { id: 'l' }
    problem[:services].each{ |service|
      service[:quantities] = [{ unit_id: 'kg', value: 1 }, { unit_id: 'l', value: -1}]
    }
    problem[:vehicles].each{ |vehicle|
      vehicle[:capacities] = [{ unit_id: 'kg', limit: 3 }, { unit_id: 'l', limit: 2}]
    }

It would be nice to make the sign dependent on the service index to have a real mix