core: use batched subscriptions (#818)

* core: use batched subscriptions

* update simplexmq

* remove comments

* clean up

* refactor

* remove todo

* revert change

* revert change

* remove comment

* add delay to the async group test

* add more delay in test

tests/ChatClient.hs

@@ -274,7 +274,8 @@ serverCfg =
       certificateFile = "tests/fixtures/tls/server.crt",
       logStatsInterval = Just 86400,
       logStatsStartTime = 0,
-      serverStatsFile = Nothing,
+      serverStatsLogFile = "tests/smp-server-stats.daily.log",
+      serverStatsBackupFile = Nothing,
       smpServerVRange = supportedSMPServerVRange
     }