cubicweb #2897696 Session raise too wide Exception when Closed [validation pending]

We have a SessionClosedError to be used instead of Exception.

prioritynormal
typebug
done in3.17.1
load0.250
load left0.000
closed by#81a5d57d9230 [session] upgrade session closed error from Exception to SessionClosedError
patch[session] Iupgrade session closed error from Exception to SessionClosedError [applied]