cubicweb #345306 refactor yams inheritance handling [open]

currently it's a bit messy (see the rebuild-inference trick in cw that I would like to avoid).

IMO it could be better if :

  • [yams] consider all relations obtained by inheritance as 'inferred'
  • [cw] trigger an event when some new inferred relation is found
  • [cw] eventually do necessary db schema changes on this event
  • [cw] be strict about removing a parent class while some children class are left in
  • [cw] remove the rebuild-inference trick

of course i am not sure about all that, it would be too easy ;)

notice though that it may work "well enough" right now, though I suspect that it'll fail in some dark corners...

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