[server] improve TZDatetime support
by depending on logilab-database 1.15.0 including
https://www.logilab.org/ticket/1485893, we can now keep the tzinfo
attribute on datetime objects for TZDatetime attributes, so one knows
that this is a tz-aware datetime.
To easily make it work with backends that have no tz support, we keep
converting tz-aware datetime objects into utc naive datetime objects
before sending them to the database.
TACHES
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-- écrire objet stocke/manipule les données
-- extraire tests de chaîne de caractère
* utiliser sqlite
* écrire fonction prend chemin en argument et renvoie contenu
* extraire tests (chaîne de caractère) de spec
* utiliser yams pour schéma