cubicweb #15538359 bad index manipulation in the massive import store [validation pending]

constraints and indexes are dropped at store creation time, but we usually want to do some query between that time and time where the import starts (eg init extid2eid dict).

prioritynormal
typebug
done in3.24.0
load left0.000
closed by#5b535fe2f364 [massive store] Lazy removal of constraints and metadata indexes
patch[massive store] Lazy removal of constraints and metadata indexes [applied][massive store] Rework constraint/index handling [applied][massive store] Lazy removal of constraints and metadata indexes [rejected]