JARM probes are crafted ClientHellos with weird ciphers — they never
complete a real handshake, so the peer cert isn't reachable from
those sockets. After a non-empty JARM hash proves the port speaks
TLS, do a separate ssl.wrap_socket() against the same (ip, port) to
fetch and parse the leaf cert.
- decnet/prober/tlscert.py: fetch + parse via cryptography lib;
swallows all connect/handshake/parse failures (returns None).
- decnet/prober/worker.py::_capture_tls_cert: emits a tls_certificate
event with subject_cn / issuer / SANs / validity / SHA-256 +
publishes on the bus. Wired from _jarm_phase only when JARM
succeeds, so non-TLS ports never trigger a second connect.
- Tests cover happy path, cert-fetch failure, defense-in-depth crash,
empty-JARM skip, publish_fn, and parser edge cases (garbage DER,
empty bytes, missing SAN extension, non-self-signed).