This commit changes LastSubscribedAtListener to pass a copy of the Carbon
object representing the current time to the SubscriberEntity property
lastSubscribedAt. Passing a copy instead of the object itself is needed to
avoid unexpected side effects. Before this change, modifying the time
of this property of a given SubscriberEntity instance could affect the
same field of another instance as the same object used inside
LastSubscribedAtListener for all entities.
[MAILPOET-3946]
c701f02d27