Unnecessary heap allocation in mandelbrot/2.cs
Why is this here?
https://github.com/hanabi1224/Programming-Language-Benchmarks/blob/1a0aea4c2917e37aea6a40c58bc6481f6ed52fdc/bench/algorithm/mandelbrot/2.cs#L52

Rest of the code assumes 256bit (4 doubles) vectors and
So this is equivalent of just calling  
```C#
 var ci = new Vector<double>(civ); 
```
Just with heap allocation of new array each call :/

Same constructor overload `new Vector<double>(0);` (I would use `Vector<double>.Zero` but the performance impact will be negligible) is used in the zeroing of all other vectors so the heap allocation seems odd.