Add a rend cache failure info dup function

When validating a new descriptor against our rend cache failure, we were
added the failure entry to the new cache entry without duplicating. It was
then freed just after the validation ending up in a very bad memory state
that was making tor abort(). To fix this, a dup function has been added and
used just before adding the failure entry.

Fixes #17041

Signed-off-by: David Goulet <dgoulet@ev0ke.net>