cubicweb #3544430 [cache] introduce a cache API and some implementations [rejected]

We will soon need to be able to cache values using various backends (e.g. database, memcached), and we need a clearly defined API. We also will provide some implementations for common cases.

This will serve the needs of sessions handling (and other cache uses) with many out-of-process web workers.

done in3.21.0
load left0.000
closed by<not specified>
patch[cache] introduce the simplest possible cache api [rejected][web] rename user -> login [rejected][cache] introduce dogpile cache for some standard cache implementations [rejected][cache] replace plain python dict with in-memory session cache [rejected]