wrap allows to define a JsonFormat[T] from a JsonFormat[U]
given a function that transforms an instance of T to an instance of
U.
Given an instance i of T, asSingleton will create a JsonFormat[T]
that will not generate any trying to serialize a T and always
return i when trying to decode an instance a T.
wrapallows to define aJsonFormat[T]from aJsonFormat[U]given a function that transforms an instance ofTto an instance ofU.iofT,asSingletonwill create aJsonFormat[T]that will not generate any trying to serialize aTand always returniwhen trying to decode an instance aT.