Maybe use a faster map for the utilities?

[Convery]

While the plugins aren't doing anything performance-critical, and will probably implement their own utilities if they do: a little performance improvement for 500 plugins can have a nice impact. We should thus consider if we want to ship with a drop-in replacement for std::unordered_map, like flat_hash_map.

std::unordered_map   - 0m5.1s
ska::flat_hash_map   - 0m2.7s