Manage concurrency
Currently (in the cache branch), only one worker is allowed.

We want to have multiple workers, but for that we need to have a shared cache:

- [ ] migrate from diskcache to redis
- [ ] remove the hardcoded limit of 1 worker
Manage concurrency: Currently (in the cache branch), only one worker is allowed.

We want to have multiple workers, but for that we need to have a shared cache:

- [ ] migrate from diskcache to redis
- [ ] remove the hardcoded limit of 1 worker