StatusCodeProbe
Inherits ProbeConcurrency < Reference < Object
Fills in details.status_code for every endpoint (--status-codes) and
drops the ones whose code the user excluded (--exclude-codes).
Deliberately not a Deliver subclass, even though it is the other thing in
noir that fires HTTP requests at discovered endpoints. A status probe runs
before delivery, ignores --probe-match / --probe-skip, and sends none of
the --probe-header values — it exists to answer "does this route respond,
and with what", not to replay traffic. Inheriting the sender base would
quietly give it all three.