Add new alternative task schedulers to benches

[Gerold103]

Currently the benches run for mg::serverbox::TaskScheduler and for a trivial lock-based scheduler without any features. Would be interesting to implement a scheduler similar to mg::serverbox::TaskScheduler in terms of feature set but also lock-based. At least its queues should be lock-based. Don't even need to actually implement those features. Should be enough to split front- and ready-queues and have a dedicated sched-role.

Another idea would be to introduce a version of the task scheduler which has a dedicated thread just for scheduling. Without the migrating sched-role like now. So its thread count is always +1 compared to mg::serverbox::TaskScheduler and this additional thread just manages the queues.

Both these new schedulers would be quite close to the serverbox's one in a sense that potentially they could have all the same features like a binary heap with waiting tasks, task wakeups, and all.