Session-recovery robustness (from PR #1)

- Suppress ConnectionError log noise from in-flight requests draining
  after a session close (poll_scheduler + keepalive log at DEBUG).
- Null KeepaliveTask.on_unreachable during a forced reconnect so the
  dying session's keepalive can't flip HA availability offline after
  the new session is already healthy. Ported into PR #5's
  _maybe_force_reconnect flow.

Drops the _session_stop / publish-health force-close mechanism from
the original PR — PR #5's last_success_ts + _maybe_force_reconnect
already covers the 'session dead, restart it' goal via a different
path, and running both means two paths force-closing the same session
on the same failure.

samsung_appliance/bridge.py

@@ -409,6 +409,11 @@ class PushBridge:
         self.log.warning(
             "unreachable for %.0fs — forcing session reconnect", elapsed)
         self._force_close_in_flight = True
+        # Null the dying session's on_unreachable so its keepalive thread
+        # can't flip availability offline after the new session takes over.
+        ka = self.keepalive
+        if ka is not None:
+            ka.on_unreachable = None
         try:
             sess.close()
         except Exception as e: