Function collection_bonus

pub fn collection_bonus(
    config: &GameConfig,
    entity_state: &EntityState<'_>,
) -> f64

B_collection — the summed contribution of the whole collection, as a fraction (0.08 is the +8% the current catalog is budgeted for).

Split out from collection_stat_mods because it is the number the UI shows and the tests assert on; the mod pairs are just its delivery.