In #1854 we switched to a Thread here to prevent the pile-up case, however under concurrent load this incurs a 10-11% penalty given backlogs aren't all that uncommon (due to the lock contention case). In .NET 6.0+, let's use the thread pool growth semantics to handle the stall case and use the cheaper Task.Run() approach.

In #1854 we switched to a `Thread` here to prevent the pile-up case, however under concurrent load this incurs a 10-11% penalty given backlogs aren't all that uncommon (due to the lock contention case). In .NET 6.0+, let's use the thread pool growth semantics to handle the stall case and use the cheaper `Task.Run()` approach.

Running the benchmarks from #1164 I was experimenting with on lock perf, I noticed a large perf sink in thread creation as a result of lock contention. For that benchmark as an example (high concurrent load) we're talking about a ~93 second -> ~84 second run reduction and similar wins in concurrent load tests.