IObject deserialize seems to resize too many times....

[gkorland]

Checking IValue::deserialize it seems like visit_map does try to allocate the IObject::with_capacity but still every call to
HeaderMut::entry also calls to IObject::resize_internal.

Which I would expect should be avoided when set with capacity.

[Diggsey]

Not all deserializers provide a size hint. But the size of the object should double each time, so it shouldn't be the case that every call to insert should result in a resize.