fix: four real defects the fourteen failing tests were pointing at

Closes netork#115.

The suite had been red long enough that it stopped being read. Four of the
fourteen failures were the tests being right.

`interfaces_mixin.py` used `re.match` without importing `re`, so
`get_mac_address_table` raised NameError against any node with a Linux bridge.
The tests never reached that line: they mocked the API call underneath
`_exec_ssh_command`, which takes two positional arguments where the doubles
accepted one, and which base64-wraps the command — so a fixture keyed on
"bridge fdb" appearing in the text matched nothing and the helper returned "".
They mock `_exec_ssh_command` itself now, which is the driver's own seam.

`is_alive` called `_resolve_node()`, which returns early without touching the
API whenever a node was configured through optional_args. A dead connection
reported itself alive. It probes `GET /version` now.

The documented `realm` optional_arg was read into `self._realm` in `__init__`
and then never used. Proxmox authenticates against "<user>@<realm>" and rejects
a bare username, so the option had no effect and callers had to know to type the
realm themselves.

`get_vlans` filtered out entries with no member ports on one return path while
the OVS path returned them, so a configured SDN VNet was visible or invisible
depending on which branch ran. A VNet exists on the node whether or not anything
is attached to it, and netOrk's VLAN discovery reads this.

`get_ipv6_neighbors_table` was simply missing and fell through to NAPALM's stub;
it is implemented against `ip -6 neigh show`, dropping FAILED entries.

The rest were stale tests. The DNS fixture put an FQDN where a search domain
belongs, which made `get_facts` build "pve1.pve1.example.com" and look like a
driver bug. The LLDP fixture was a simplified shape that real `lldpcli show
neighbors summary` does not produce — the parser matches on the ", via: LLDP"
that follows the interface name. And `test_bridge_vlan_show_parsing` covered a
fallback that was replaced by VM-config scanning, asserting an "interfaces" key
this method has never returned; it is now a test of the fallback that exists.

tests/test_misc.py

@@ -263,18 +263,29 @@ class TestGetRouteTo:
 
 
 class TestLLDPNeighbors:
+    # Real `lldpcli show neighbors summary` output. The interface line carries
+    # ", via: LLDP, ..." after the name, which is what the parser matches on —
+    # the previous fixture stopped at the name and matched nothing.
     LLDP_SUMMARY = (
-        "  Interface: eth0\n"
-        "    SysName: sw01.example.com\n"
-        "    PortID: ifname GigabitEthernet1/0/1\n"
-        "  Interface: eth1\n"
-        "    SysName: sw02.example.com\n"
-        "    PortID: ifname GigabitEthernet1/0/2\n"
+        "LLDP neighbors:\n"
+        "-------------------------------------------------------------------------------\n"
+        "Interface:    eth0, via: LLDP, RID: 1, Time: 0 day, 00:11:22\n"
+        "  Chassis:\n"
+        "    SysName:      sw01.example.com\n"
+        "  Port:\n"
+        "    PortID:       ifname GigabitEthernet1/0/1\n"
+        "-------------------------------------------------------------------------------\n"
+        "Interface:    eth1, via: LLDP, RID: 2, Time: 0 day, 00:11:22\n"
+        "  Chassis:\n"
+        "    SysName:      sw02.example.com\n"
+        "  Port:\n"
+        "    PortID:       ifname GigabitEthernet1/0/2\n"
+        "-------------------------------------------------------------------------------\n"
     )
 
     def test_neighbors_found(self, driver):
-        driver._node_api().execute.post.return_value = {"data": self.LLDP_SUMMARY}
-        result = driver.get_lldp_neighbors()
+        with patch.object(driver, "_exec_ssh_command", return_value=self.LLDP_SUMMARY):
+            result = driver.get_lldp_neighbors()
         assert "eth0" in result
         assert result["eth0"][0]["hostname"] == "sw01.example.com"