`<string>` doesn't seem to be required at all and `flat_map` doesn't support `vector<bool>`, so we can include just `vector<T>`. This cuts the include time in half on my system.
`<string>` doesn't seem to be required at all and `flat_map` doesn't support `vector<bool>`, so we can include just `vector<T>`. This cuts the include time in half on my system.