feat(ping): implement ping and a batched ping_sweep over the diagnostics API

OPNsense has no synchronous ping endpoint. /api/diagnostics/ping is a job API —
create, start, read statistics, stop, remove — so a single ping costs five
requests and roughly a second of waiting, which makes the generic per-host
sweep from napalm-device-types unusable for a whole subnet.

The override exploits what the job API does offer instead: jobs are
independent and run on the firewall in parallel, and search_jobs reports all of
them in one response. A batch (32 by default) is created and started, waited
for once, harvested with a single request and then cleaned up, so waiting time
per batch is constant rather than linear in hosts. PING_SWEEP_MAX_TARGETS
bounds the sweep as a whole — this runs on production firewalls.

Two details the API forces: results are polled, because search_jobs signals the
running ping with SIGINFO and then parses whatever it has written so far, so
the first read of a healthy host can still show zero probes; and the model's
root node is read from /get rather than hardcoded, so a rename in a future
OPNsense release cannot silently break job creation.

Tested against mocked API responses only — no live device is reachable at the
moment, so the endpoint shapes come from the OPNsense sources (PingController,
scripts/interfaces/ping.py).

napalm_opnsense/opnsense.py

@@ -50,8 +50,10 @@ from requests.exceptions import RequestException
 from napalm_device_types import FingerprintRule, FirewallDriver
 from napalm.base.exceptions import ConnectionException, ConnectionClosedException, MergeConfigException
 
+from napalm_opnsense.ping_mixin import OPNsensePingMixin
 
-class OPNsenseDriver(FirewallDriver):
+
+class OPNsenseDriver(OPNsensePingMixin, FirewallDriver):
     """NAPALM driver for OPNsense (read-only, REST API)."""
 
     VENDOR = "OPNsense"