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/parse.py

@@ -257,3 +257,93 @@ def boottime(text: str) -> Optional[int]:
     """``sysctl -n kern.boottime``: FreeBSD ``{ sec = N, … }``, OpenBSD ``N``."""
     match = re.search(r"sec = (\d+)", text) or re.fullmatch(r"\s*(\d+)\s*", text)
     return int(match[1]) if match else None
+
+
+def _socket(
+    proto: str, local: str, family: str, process: Optional[str], pid: Optional[int]
+) -> Optional[dict[str, Any]]:
+    """A ListeningSocketDict from a local endpoint: ``*:22``, ``[::1]:25``,
+    ``127.0.0.1:25``, ``[fe80::1%lo0]:25`` (sockstat, fstat) or ``*.22``,
+    ``::1.25``, ``fe80::1%lo0.25`` (netstat)."""
+    if local.startswith("["):
+        address, _, port = local[1:].partition("]:")
+    elif local.count(":") == 1 or local.startswith("*:"):
+        address, _, port = local.rpartition(":")
+    else:
+        address, _, port = local.rpartition(".")
+    if not port.isdigit() or int(port) == 0:
+        return None
+    address, _, zone = address.partition("%")
+    if address == "*":
+        address = "0.0.0.0" if family == "4" else "::"
+    return {
+        "proto": proto,
+        "address": address,
+        "port": int(port),
+        "interface": zone or None,
+        "process": process,
+        "pid": pid,
+        "unit": None,
+        "container_id": None,
+    }
+
+
+def _unique(sockets: list[Optional[dict[str, Any]]]) -> list[dict[str, Any]]:
+    """One entry per socket, the first process holding it, as ss reports it."""
+    seen: set[tuple] = set()
+    result = []
+    for s in sockets:
+        if s is None:
+            continue
+        key = (s["proto"], s["address"], s["port"], s["interface"])
+        if key not in seen:
+            seen.add(key)
+            result.append(s)
+    return result
+
+
+def sockstat(text: str) -> list[dict[str, Any]]:
+    """FreeBSD ``sockstat -46lq -P tcp,udp``: USER COMMAND PID FD PROTO LOCAL FOREIGN."""
+    sockets = []
+    for line in text.splitlines():
+        words = line.split()
+        if len(words) < 7 or not words[2].isdigit() or words[4][:3] not in ("tcp", "udp"):
+            continue
+        proto, family = words[4][:3], words[4][3:]
+        sockets.append(_socket(proto, words[5], family, words[1], int(words[2])))
+    return _unique(sockets)
+
+
+def fstat_sockets(text: str) -> list[dict[str, Any]]:
+    """OpenBSD ``fstat -n``: the internet sockets nothing is connected to.
+
+    ``USER CMD PID FD internet[6] stream|dgram tcp|udp [0xPCB] LOCAL [ARROW REMOTE]``;
+    a socket with an arrow is connected, one bound to port 0 is not bound.
+    """
+    sockets = []
+    for line in text.splitlines():
+        words = line.split()
+        if len(words) < 8 or words[4] not in ("internet", "internet6"):
+            continue
+        if any(arrow in words for arrow in ("<--", "-->", "<->")):
+            continue
+        family = "6" if words[4] == "internet6" else "4"
+        sockets.append(_socket(words[6], words[-1], family, words[1], int(words[2])))
+    return _unique(sockets)
+
+
+def netstat_listening(text: str) -> list[dict[str, Any]]:
+    """``netstat -an``: listening TCP and bound UDP sockets, without their process."""
+    sockets = []
+    for line in text.splitlines():
+        words = line.split()
+        if len(words) < 5 or words[0][:3] not in ("tcp", "udp"):
+            continue
+        proto, family = words[0][:3], "6" if words[0].endswith("6") else "4"
+        local, foreign = words[3], words[4]
+        if proto == "tcp" and words[-1] != "LISTEN":
+            continue
+        if proto == "udp" and foreign != "*.*":
+            continue
+        sockets.append(_socket(proto, local, family, None, None))
+    return _unique(sockets)