Add more options for `BM_iteration` in order to see better picture for choosing trade off for iteration optimizations.

```
BM_Iteration/1/1      1.83ns ± 0%
BM_Iteration/2/2      2.63ns ±11%
BM_Iteration/4/4      5.76ns ±26%
BM_Iteration/7/7      3.79ns ± 0%
BM_Iteration/10/10    8.49ns ±23%
BM_Iteration/15/15    18.2ns ±30%
BM_Iteration/16/16    21.2ns ±29%
BM_Iteration/54/54    37.2ns ±21%
BM_Iteration/100/100  74.7ns ±13%
BM_Iteration/400/400   330ns ± 8%
BM_Iteration/0/0      0.46ns ± 2%
BM_Iteration/10/0     1.26ns ± 1%
BM_Iteration/100/0    13.4ns ± 0%
BM_Iteration/1000/0    417ns ± 0%
BM_Iteration/10000/0  3.30µs ± 0%
BM_Iteration/100/1    16.0ns ±12%
BM_Iteration/1000/10   453ns ± 5%
```

PiperOrigin-RevId: 474282700
Change-Id: I4b3fcb80292147aa4a8f542ae5c7fc1e8bd5f05b