Add support for declearn Vector instances in Serializer
Currently, fedbiomed.common.serializer.Serializer
does not support (de)serialization declearn Vector
(subclasses) instances, which poses an issue to share fedbiomed.common.optimizers.Optimizer
auxiliary variables across network.
This will easily be solved, but I open this issue to keep track of our tackling it (and provided with a reference to name the associated branch).