feat: report listening sockets

get_listening_sockets() in the shape of napalm-device-types'
ListeningSocketsMixin, whose ss/cgroup reading is Linux's, and with its
rule: read as root first, and without root when that brings nothing back,
which the reading reports as `attributed: False`.

- FreeBSD: `sockstat -46lq -P tcp,udp`, which sees every socket either way.
- OpenBSD: `fstat -n` as root (the sockets nothing is connected to; port 0
  is unbound), `netstat -an` without root, as fstat shows a user only
  their own processes; those sockets come without a process.
- Addresses as ss prints them: `*` becomes 0.0.0.0 or :: by family, IPv6
  without brackets, a zone (`fe80::1%lo0`) becomes the interface. One entry
  per socket, the first process holding it.

No get_kernel_facts on purpose: KernelFactsMixin reports a Linux kernel's
modules and CONFIG_ options, which a BSD kernel does not have.

Fixtures recorded on the FreeBSD 15.1 and OpenBSD 7.9 VMs with test
listeners on 127.0.0.1 and ::1 (NetOrk/netork#798).

napalm_bsd/freebsd.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from napalm_device_types import FingerprintRule
 
+from napalm_bsd import parse
 from napalm_bsd.base import BsdDriver
 
 
@@ -28,6 +29,11 @@ class FreeBSDDriver(BsdDriver):
     )
     # -W: FreeBSD cuts long destinations to the column width otherwise.
     ROUTES_COMMAND = "netstat -rnW"
+    # sockstat names the process of every socket it can see; root sees them all.
+    LISTENING_COMMAND = "sockstat -46lq -P tcp,udp"
+
+    def _parse_listening(self, output: str, *, attributed: bool) -> list[dict]:
+        return parse.sockstat(output)
 
     def _os_version(self) -> str:
         version = super()._os_version()