backend: store adaptive rate changes as events and serve an audit of them per line

backend/tests/MoShiro.TestSupport/AgentSimulator.cs

@@ -223,6 +223,13 @@ public sealed class AgentSimulator : IAsyncDisposable
             new HeartbeatParams { Extra = JsonSerializer.SerializeToElement(new NodeHeartbeatExtra { Update = status }, MoShiroJsonContext.Default.NodeHeartbeatExtra) },
             FleetRpcContext.Default.HeartbeatParams));
 
+    /// <summary>像拨号节点那样，随心跳上报自适应探测频率的状态变化。</summary>
+    public Task SendRateChangesAsync(params RateChange[] changes) =>
+        SendAsync(RpcMessage.Notification(
+            FleetMethods.Heartbeat,
+            new HeartbeatParams { Extra = JsonSerializer.SerializeToElement(new NodeHeartbeatExtra { RateChanges = [.. changes] }, MoShiroJsonContext.Default.NodeHeartbeatExtra) },
+            FleetRpcContext.Default.HeartbeatParams));
+
     public async Task<RpcMessage> RequestRawAsync(string method, JsonElement? parameters = null) => await RequestAsync(method, parameters);
 
     public async Task<TaskSet> WaitForTaskSetAsync(Func<TaskSet, bool> predicate, TimeSpan? timeout = null)