feat: get_system_identity for matching a node to its BMC (0.2.0)

Mixes in napalm-device-types 4.9's SystemIdentityMixin over the exec
path, which runs as root: the node's SMBIOS system UUID, product serial
and board serial, vendor placeholders empty. pve-dual, a Supermicro
X10DRL-i, reports the product serial 0123456789; its board serial and
UUID are what tie it to its BMC.

tests/test_system_identity.py

@@ -0,0 +1,31 @@
+"""`get_system_identity`: the node's SMBIOS identity, what ties it to its BMC.
+
+The command, its parse and the placeholder filter are napalm-device-types'; the driver
+only carries the command over its exec path, which runs as root.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import patch
+
+from napalm_device_types import SYSTEM_IDENTITY_COMMAND, SystemIdentityMixin
+from napalm_proxmox.driver import ProxmoxDriver
+
+# pve-dual, a Supermicro X10DRL-i: the product serial is the board vendor's default.
+WIRE = "IDBEGIN\n31303043-534D-C40C-7A72-6F1300000000\n0123456789\nZM155S026022\nIDEND\n"
+
+
+def test_the_driver_declares_the_contract():
+    assert issubclass(ProxmoxDriver, SystemIdentityMixin)
+
+
+def test_it_runs_the_shared_command(driver):
+    with patch.object(driver, "_exec_ssh_command", return_value=WIRE) as exec_:
+        identity = driver.get_system_identity()
+
+    exec_.assert_called_once_with(SYSTEM_IDENTITY_COMMAND)
+    assert identity == {
+        "system_uuid": "31303043-534d-c40c-7a72-6f1300000000",
+        "product_serial": "",
+        "board_serial": "ZM155S026022",
+    }