fix: tolerate agent events with missing host in neutron-ovn-operator

neutron-ovn-operator polls openstack network agents and diffs it against the previous poll, keyed by agent host.

Neutron derives on OVN agent's host from the Southbound DB via Chassis_Private -> Chassis. When these two fall out of sync - for example an ungraceful ovn-controller restart, or because a neutron-server worker's in-memory AgentCache missed an update, which might lead to lookup fails and the task will crash as following:

Before fix

2026-09-01 13:04:19,222   DEBUG  yaook.op.daemon  dispatching external EventType.DELETED event on object None of type <class 'yaook.statemachine.resources.openstack.NeutronAgentWatcher'>
2026-09-01 13:04:19,223   ERROR  yaook.op.tasks.RestartingTask.136077189427024  task crashed! retrying in 1s
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/yaook/op/tasks.py", line 555, in _task_done
    result = task.result()
             ^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/yaook/op/daemon.py", line 954, in _watch_external
    self._dispatch_external_event(api, watcher, ev)
  File "/usr/local/lib/python3.11/site-packages/yaook/op/daemon.py", line 1299, in _dispatch_external_event
    self._deliver_event(
  File "/usr/local/lib/python3.11/site-packages/yaook/op/daemon.py", line 972, in _deliver_event
    trigger_reconcile = func(ctx, event)
                        ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/yaook/statemachine/resources/openstack.py", line 1169, in _handle_agent_event
    if event.object_.host != ctx.parent_name:
       ^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'host'
2026-09-01 13:04:20,227    INFO  yaook.op.daemon  setting up watcher for <class 'yaook.statemachine.resources.openstack.NeutronAgentWatcher'>

This change adds a prober error handling when event.object_ is None or has no host

After fix:

2026-09-01 16:23:30,922   DEBUG  yaook.op.daemon  dispatching external EventType.DELETED event on object None of type <class 'yaook.statemachine.resources.openstack.NeutronAgentWatcher'>
2026-09-01 16:23:30,922 WARNING  yaook.op.daemon  Event for object compute02 has no host set. Abort the handling of the event.
2026-09-01 16:23:30,925   DEBUG  yaook.op.tasks  nothing to do, waiting for something to happen
2026-09-01 16:23:30,925   DEBUG  yaook.op.tasks  nothing to do, waiting for something to happen