Consider restoring previous signal handler on stop if its not `SIG_DFL`

[korniltsev-grafanista-yolo-vibecoder239]

In #8 we restored signal handler to SIG_IGN

However, maybe we should have restored to SIG_IGN only if the previous is SIG_DFL, otherwise if there was another handler, we should have restored it.
Not a big problem (until it breks someone elses code).