added EventStreamBenchmark

[Aaronontheweb]

Changes

Added some benchmarks to clock the throughput of the EventStream before we consider making some changes to it.

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 dev Benchmarks

BenchmarkDotNet=v0.13.2, OS=Windows 10 (10.0.19044.2486/21H2/November2021Update)
AMD Ryzen 7 1700, 1 CPU, 16 logical and 8 physical cores
.NET SDK=7.0.100
  [Host]     : .NET 7.0.0 (7.0.22.51805), X64 RyuJIT AVX2
  Job-JPMJGS : .NET 7.0.0 (7.0.22.51805), X64 RyuJIT AVX2

InvocationCount=1  UnrollFactor=1  

Method	Mean	Error	StdDev	Allocated
Publish	54.90 ns	0.498 ns	0.441 ns	-