Function secondary_optional_cost 

pub fn secondary_optional_cost<S>(
    spell: &SpellDataFlat,
    secondary_resource_type: Option<i32>,
    modifiers: &PowerModifiers,
    active_aura_spell_ids: &HashSet<i32, S>,
) -> f64
where
    S: BuildHasher,

Optional secondary power cost above the minimum (for variable-point finishers).