We need to determine the optimal set of routes for a fleet of vehicles to deliver goods to a set of customers.
Each route must stard and end at the depot.
The objective is to minimize the total travel distance while ensuring all deliveries are made without exceeding vehicle capacities.

Example input data:
1. vehicles.csv
vehicle_id,capacity
1,15
2,15

2. customers.csv
customer_id,location,demand
1,LocA,5
2,LocB,7
3,LocC,4
4,LocD,6

3. distances.csv
from,to,distance
Depot,LocA,5
Depot,LocB,10
Depot,LocC,7
Depot,LocD,3
LocA,LocB,6
LocA,LocC,8
LocA,LocD,4
LocB,LocC,2
LocB,LocD,5
LocC,LocD,3