Warn when cache computation is cheaper than cache retrival

[pi0]

(From question by @InstantlyMoist in #2558)

In development mode, we can detect situations when cache computation is cheaper than storing and retrieving it to warn users about it. It is not a precise prediction though because in production (when cache might be stored externally to disk or a remote server and database/server load is heavier than single user local/staging, the cache would make sense so maybe if we do it, we should do it for dev and prod)