Register an event with all servers.

        Args:
            direction (str): `in`, `out`, `both`, `raw`.
            verb (str): Event name.
            child_fn (function): Handler function.
            priority (int): Handler priority (lower priority executes first).

def register_event(self, direction, verb, child_fn, priority=10):
        """Register an event with all servers.

        Args:
            direction (str): `in`, `out`, `both`, `raw`.
            verb (str): Event name.
            child_fn (function): Handler function.
            priority (int): Handler priority (lower priority executes first).
        """
        if verb not in self._event_handlers:
            self._event_handlers[verb] = []

        self._event_handlers[verb].append({
            'handler': child_fn,
            'direction': direction,
            'priority': priority,
        })

        for name, server in self.servers.items():
            server.register_event(direction, verb, child_fn, priority=priority)