fix(opcuaclient): don't count idle-session BadNoSubscription as a publish error (lmxopcua#764)

The SDK keeps sending publish requests on a session that holds no subscription,
and the server answers each with an anonymous (id 0) BadNoSubscription. With
nothing tracked there is nothing to lose, but every answer was counted on
publish_error, so the counter climbed on any idle driver. HandlePublishError now
returns before counting for an anonymous BadNoSubscription while neither the data
nor the alarm subscription set tracks anything. Any other PublishError, and an
anonymous one while something is tracked, is counted and handled as before.

Not addressed from #764: the Republish/state probe for a delete slower than the
5 s grace, and the #728 wire test's fixed delays.

Tests: OpcUaClientIdlePublishErrorTests (idle session: not counted, with a
BadTooManyPublishRequests positive control; tracked subscription: still counted).
The idle test fails without the fix. Driver.OpcUaClient.Tests 295/0.
Docs: drivers/OpcUaClient.md.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

docs/drivers/OpcUaClient.md

@@ -357,7 +357,9 @@ Session/publish events are published on the shared OTel meter as the counter
 `keepalive_miss`, `keepalive_recovered` (a bad keep-alive followed by a good one on the same session),
 `stale_notification_dropped` (a late replay dropped inside the post-recovery window, see above). A climbing
 `keepalive_miss` / `keepalive_recovered` rate is the signature of a flapping upstream (`reconnect_*` were removed with
-the reconnect handler, #670). They are not part of `DriverHealth` or the
+the reconnect handler, #670). `publish_error` does not count the anonymous `BadNoSubscription` a server returns
+while the driver tracks no subscription at all — the SDK keeps publishing on an idle session, so that is noise (#764).
+They are not part of `DriverHealth` or the
 `/hosts` panel.
 
 ## Testing