This commit reworks the Sniffer component to simplify it and make it possible to test it.
In particular, it no longer takes out the host that failed when sniffing on failure, but rather relies on whatever the cluster returns. This is the result of some valid comments from #27985. Taking out one single host is too naive, hard to test and debug.
A new Scheduler abstraction is introduced to abstract the tasks scheduling away and make it possible to plug in any test implementation and take out timing aspects when testing.
Concurrency aspects have also been improved, synchronized methods are no longer required. At the same time, we were able to take #27697 and #25701 into account and fix them, especially now that we can more easily add tests.
Last but not least, unit tests are added for the Sniffer component, long overdue.
Closes#27697Closes#25701
63f3a61134