Cost optimization

Currently, the Ruby script optimizes with respect to material (`P`) and dimensions of the Arm (`V`). This should be extended to optimize with respect to total cost of materials as well, ie, via Multi-objective optimization.

Start by locating the Ruby script and reading how its current optimization uses material (P) and Arm dimensions (V). Determine the intended total-material-cost objective and how it should participate in the multi-objective optimization. Done means the script accounts for total material cost alongside the existing objectives.

Written by the indexing model from the issue text.