Function RestoreMobileUserFlows

Puts back the flows a checkpoint carries: the restored process continues the flows the checkpointed one was running, with their start times, so a flow the checkpointed process would have timed out times out at the same moment, and its logger is where the checkpointed process's was (a checkpoint taken inside the launch's first flight restores a process that still stamps no header). A flow whose time-to-live already ran out while the process was not running is not put back: the state holds running flows only, and the checkpoint of the restored process does not carry it either. A value of another shape is the typed CheckpointDecodeError.