loading series is really slow

[jborza]

url: series/api
maybe it's doing something it shouldn't

Or save series to a separate table, like Authors

[jborza]

Looking at the sources https://github.com/jborza/booklibrary/blob/main/series/series_routes.py#L24, maybe because we go through each serie and querying the DB and retrieving cover images?
It would be much better to fetch Book.cover_image at the first (and ideally the only) query.