Added expiration to garnet objects at time of serialization deserialization

[pradeepyadavmsft]

This fix addresses a bug where expiration is not being added to serialization, potentially causing some objects to become live again after recovery from a checkpoint.

If you are using the object store, please clean up older checkpoints as it will not be able to deserialize them due to the breaking nature of this change.

[badrishc]

The proposed serialization format is: [base class fields][derived class fields] where [base class fields] = [type][expiration]