Function select_best_assets 

pub fn select_best_assets(
    model: &Model,
    opt_assets: Vec<AssetRef>,
    candidate_investment_limits: HashMap<AssetRef, AssetCapacity>,
    commodity: &Commodity,
    agent: &Agent,
    region_id: &RegionID,
    prices: &Prices,
    demand: DemandMap,
    year: u32,
    writer: &mut DataWriter,
) -> Result<Vec<AssetRef>>

Get the best assets for meeting demand for the given commodity