feat: report what listens, and which Windows service it is

One script: Get-NetTCPConnection -State Listen, Get-NetUDPEndpoint, the
processes holding them and Win32_Service's PIDs. A process running one
service names it; a shared svchost runs several, and which of them holds
the socket Windows does not say, so it names none. http.sys sockets
(WinRM, IIS, SMB) belong to the System process.

The fixture is synthetic: no Windows host was at hand. tools/harvest.py
records the real output. For netOrk#673.

tests/fixtures/synthetic/listening.json

@@ -0,0 +1,31 @@
+{
+  "tcp": [
+    {"address": "0.0.0.0", "port": 135, "pid": 912},
+    {"address": "::", "port": 135, "pid": 912},
+    {"address": "0.0.0.0", "port": 445, "pid": 4},
+    {"address": "0.0.0.0", "port": 5985, "pid": 4},
+    {"address": "0.0.0.0", "port": 3389, "pid": 1180},
+    {"address": "0.0.0.0", "port": 1433, "pid": 4321},
+    {"address": "127.0.0.1", "port": 1434, "pid": 4321},
+    {"address": "fe80::1c2a:3b4c:5d6e:7f80%12", "port": 1433, "pid": 4321}
+  ],
+  "udp": [
+    {"address": "0.0.0.0", "port": 123, "pid": 1404},
+    {"address": "::", "port": 123, "pid": 1404},
+    {"address": "0.0.0.0", "port": 5353, "pid": 0}
+  ],
+  "processes": [
+    {"pid": 4, "name": "System"},
+    {"pid": 912, "name": "svchost"},
+    {"pid": 1180, "name": "svchost"},
+    {"pid": 1404, "name": "svchost"},
+    {"pid": 4321, "name": "sqlservr"}
+  ],
+  "services": [
+    {"pid": 912, "name": "RpcEptMapper"},
+    {"pid": 912, "name": "RpcSs"},
+    {"pid": 1180, "name": "TermService"},
+    {"pid": 1404, "name": "W32Time"},
+    {"pid": 4321, "name": "MSSQL$SQLEXPRESS"}
+  ]
+}