pub fn get_nearby_mergeable_items<'a>(
    item: &'a PickupItem,
    pos: &'a Pos,
    loot_owner: Option<&'a LootOwner>,
    (entities, items, positions, loot_owners, spatial_grid): (&'a Entities<'a>, &'a WriteStorage<'a, PickupItem>, &'a ReadStorage<'a, Pos>, &'a ReadStorage<'a, LootOwner>, &'a CachedSpatialGrid)
) -> impl Iterator<Item = (Entity, f32)> + 'a