MaxEncodedLen have a statically known maximum encoded size.
Some containers, such as
BoundedVec, have enforced size limits and this trait
can be implemented accurately. Other containers, such as
StorageMap, do not have enforced size
limits. For those containers, it is necessary to make a documented assumption about the maximum
usage, and compute the max encoded length based on that assumption.
Upper bound, in bytes, of the maximum encoded size of this item.