move agent_token from swarm-queue-client to swarm-agent-verify

per #5471, verifiers stop depending on the queue client. the module is
store-free and needs only thiserror, so swarm-agent-verify gains one
dependency and loses its swarm-queue-client edge. consumers import it
from swarm_agent_verify; swarm-logs and swarm-metrics, whose only use of
swarm-queue-client was this module, drop that dependency, as does
swarm-logs-auth.

swarm-secret-client/src/queue.rs

@@ -24,7 +24,7 @@
 //! renewing the other.
 //!
 //! The token an agent presents that secret in at the queue is spelled by
-//! `swarm_queue_client::agent_token`, which needs no store client.
+//! `swarm_agent_verify::agent_token`.
 
 use serde::{Deserialize, Serialize};