Added Dispatcher Benchmarks

[Aaronontheweb]

Changes

Added Benchmark.NET ports of our old NBench benchmarks in order to measure memory allocation and throughput for various benchmark configurations.

Checklist

For significant changes, please ensure that the following have been completed (delete if not relevant):

• This change follows the Akka.NET API Compatibility Guidelines.
• This change follows the Akka.NET Wire Compatibility Guidelines.
• I have reviewed my own pull request.

Latest v1.4 Benchmarks

.NET 6

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.19044.2006 (21H2)
AMD Ryzen 7 1700, 1 CPU, 16 logical and 8 physical cores
.NET SDK=6.0.201
  [Host]     : .NET 6.0.3 (6.0.322.12309), X64 RyuJIT
  DefaultJob : .NET 6.0.3 (6.0.322.12309), X64 RyuJIT

Method	TaskCount	Configurator	Mean	Error	StdDev	Gen 0	Allocated
RunDispatcher	1000000	ChannelD	2,422.2 ms	17.45 ms	16.32 ms	161000.0000	641 MB
RunDispatcher	1000000	DefaultThreadPool	1,156.6 ms	43.33 ms	127.75 ms	15000.0000	61 MB
RunDispatcher	1000000	ForkJoin(remote)	658.4 ms	10.47 ms	9.79 ms	23000.0000	92 MB
RunDispatcher	1000000	ForkJoin(sys)	649.2 ms	6.33 ms	5.29 ms	23000.0000	92 MB
RunDispatcher	1000000	TaskD	1,204.3 ms	8.15 ms	7.62 ms	23000.0000	92 MB

.NET Core 3.1

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.19044.2006 (21H2)
AMD Ryzen 7 1700, 1 CPU, 16 logical and 8 physical cores
.NET SDK=6.0.201
  [Host]     : .NET Core 3.1.23 (CoreCLR 4.700.22.11601, CoreFX 4.700.22.12208), X64 RyuJIT
  DefaultJob : .NET Core 3.1.23 (CoreCLR 4.700.22.11601, CoreFX 4.700.22.12208), X64 RyuJIT

Method	TaskCount	Configurator	Mean	Error	StdDev	Median	Gen 0	Allocated
RunDispatcher	1000000	ChannelD	2,792.1 ms	10.40 ms	8.12 ms	2,790.2 ms	161000.0000	641 MB
RunDispatcher	1000000	DefaultThreadPool	1,266.9 ms	25.25 ms	71.63 ms	1,290.7 ms	15000.0000	61 MB
RunDispatcher	1000000	ForkJoin(remote)	699.4 ms	6.21 ms	5.81 ms	700.3 ms	23000.0000	92 MB
RunDispatcher	1000000	ForkJoin(sys)	696.7 ms	7.25 ms	6.78 ms	696.9 ms	23000.0000	92 MB
RunDispatcher	1000000	TaskD	1,346.5 ms	3.24 ms	3.03 ms	1,346.3 ms	23000.0000	92 MB

[Aaronontheweb]

Lots of delegate allocation in all of the dispatchers - especially the ChannelDispatcher.

[Aaronontheweb]

Some of it might also be just items being added to the work queue - not necessarily delegate allocation. Could also be some boxing allocation involved too.

[Aaronontheweb]

Reviewed my own PR

[Aaronontheweb]

Pulls out default Akka.NET dispatcher configurations, where available

[Aaronontheweb]

Try to force all operations to complete before allowing each benchmark iteration to exit