CalculateArraySum for <0-9>

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.17134.829 (1803/April2018Update/Redstone4)
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=3.0.100-preview7-012821
  [Host]     : .NET Core 3.0.0-preview7-27912-14 (CoreCLR 4.700.19.32702, CoreFX 4.700.19.36209), 64bit RyuJIT
  DefaultJob : .NET Core 3.0.0-preview7-27912-14 (CoreCLR 4.700.19.32702, CoreFX 4.700.19.36209), 64bit RyuJIT

Method	Mean	Error	StdDev	Ratio	RatioSD
WithSpan	16.28 ns	0.3585 ns	0.5990 ns	1.00	0.00
WithoutSpan	14.34 ns	0.3110 ns	0.2597 ns	0.87	0.04

SelectAndUpdateArrayItem for 10 Items

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.17134.829 (1803/April2018Update/Redstone4)
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=3.0.100-preview7-012821
  [Host]     : .NET Core 3.0.0-preview7-27912-14 (CoreCLR 4.700.19.32702, CoreFX 4.700.19.36209), 64bit RyuJIT
  DefaultJob : .NET Core 3.0.0-preview7-27912-14 (CoreCLR 4.700.19.32702, CoreFX 4.700.19.36209), 64bit RyuJIT

Method	Mean	Error	StdDev	Ratio	RatioSD
WithSpan	10.717 ns	0.3671 ns	0.4370 ns	1.00	0.00
WithoutSpan	8.474 ns	0.1594 ns	0.1491 ns	0.78	0.03

SerializeObject With System.Text.Json vs Newtonsoft.Json

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.17134.829 (1803/April2018Update/Redstone4)
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=3.0.100-preview7-012821
  [Host]     : .NET Core 3.0.0-preview7-27912-14 (CoreCLR 4.700.19.32702, CoreFX 4.700.19.36209), 64bit RyuJIT
  DefaultJob : .NET Core 3.0.0-preview7-27912-14 (CoreCLR 4.700.19.32702, CoreFX 4.700.19.36209), 64bit RyuJIT

Method	Mean	Error	StdDev	Median	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
SystemTextJson	1.225 us	0.0243 us	0.0480 us	1.206 us	1.00	0.00	0.1106	-	-	527 B
NewtonsoftJson	1.346 us	0.0258 us	0.0253 us	1.332 us	1.10	0.04	0.3338	-	-	1575 B