Abandon persisted value forget and come up with better way to express lifetime contains

[MeirShpilraien]

Persisted value should not live for a longer time than the isolate they were created on. Today we are using a forget function that basically says that the isolate will release this memory when it is destroyed. In addition, nothing forces us to keep the persisted value for a longer time then the isolate. We should come up with a better way to express those concerns.