yams #109207 [schema] rproperties: stop duck typing [validation pending]

we keep the bw compat for date/datetime/etc. to let people adjust their schemas

for other types, this should be transparent (it was cubicweb that converted back and forth default values to unicode strings)

appeared in<not specified>
done in0.39.0
load left0.000
closed by#6b7e541193f6 [schema] cleanup default values handling in entity schema (closes #109207)
patch[schema] default values: cease duck typing practice (except for date/datetimes/... for bw compat) (closes #109207) [applied]