fix(ssh): verify the host key netOrk expects, report the one seen (NetOrk/netork#1167)

The driver accepted any SSH host key. It now verifies through
napalm-device-types' HostKeyCheck (>= 4.19.0): with a known key in
optional_args["ssh_host_keys"] any other key is refused before login, and
every key seen is reported to optional_args["ssh_host_key_observer"].
Without either argument it connects as before (first use).

napalm_linux/linux.py

@@ -59,6 +59,7 @@ from napalm_device_types import (
     run_on_transport,
     strip_terminal_codes,
 )
+from napalm_device_types.ssh_host_keys import HostKeyCheck
 from napalm_device_types.models import (
     ApplyUpdatesResultDict,
     CronJobDict,
@@ -356,6 +357,8 @@ class LinuxDriver(
         # port is passed explicitly in open() — remove it from netmiko_optional_args
         # to avoid "multiple values for keyword argument 'port'"
         self.netmiko_optional_args.pop("port", None)
+        # The host key to expect, and where the one seen is reported (netork#1167).
+        self._host_key = HostKeyCheck(optional_args, hostname, self.port)
 
         # Runtime state
         self._device: ConnectHandler | None = None
@@ -368,20 +371,22 @@ class LinuxDriver(
     def open(self) -> None:
         """Open the SSH connection and detect the package manager."""
         try:
-            self._device = ConnectHandler(
-                device_type=self.NETMIKO_DEVICE_TYPE,
-                host=self.hostname,
-                username=self.username,
-                password=self.password,
-                port=self.port,
-                secret=self._secret,
-                timeout=self.timeout,
-                **self.netmiko_optional_args,
-            )
+            with self._host_key.netmiko(self.netmiko_optional_args) as netmiko_args_:
+                self._device = ConnectHandler(
+                    device_type=self.NETMIKO_DEVICE_TYPE,
+                    host=self.hostname,
+                    username=self.username,
+                    password=self.password,
+                    port=self.port,
+                    secret=self._secret,
+                    timeout=self.timeout,
+                    **netmiko_args_,
+                )
         except NetmikoAuthenticationException as exc:
             raise ConnectionException(str(exc)) from exc
         except NetmikoTimeoutException as exc:
             raise ConnectionException(str(exc)) from exc
+        self._host_key.observe(self._device.remote_conn_pre.get_transport())
 
         # No history before anything else is typed (NetOrk/netork#1039).
         try: