Multiply 128Bit in barrett reduction

[kzrnm]

BenchmarkDotNet=v0.13.4, OS=Windows 10 (10.0.19045.2486)
Intel Core i7-4790 CPU 3.60GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET SDK=7.0.101
  [Host]   : .NET 7.0.1 (7.0.122.56804), X64 RyuJIT AVX2
  ShortRun : .NET 7.0.1 (7.0.122.56804), X64 RyuJIT AVX2

Job=ShortRun  IterationCount=3  LaunchCount=1  
WarmupCount=3  

Method	Toolchain	Mean	Error	StdDev
MultiplyNoFlags	.NET 7.0	1.137 ms	0.1722 ms	0.0094 ms
MultiplyNoFlags	.NET Core 3.1	1.159 ms	0.6725 ms	0.0369 ms
Mul128Bit	.NET 7.0	2.208 ms	1.9935 ms	0.1093 ms
Mul128Bit	.NET Core 3.1	2.175 ms	0.1901 ms	0.0104 ms
Modulus	.NET 7.0	4.647 ms	0.4117 ms	0.0226 ms
Modulus	.NET Core 3.1	4.696 ms	0.6656 ms	0.0365 ms