benchmark commit step and ark counterparts (dragoon/komodo!63)

this MR adds a benchmark for
- the KZG10 trusted setup creating of `ark-poly-commit`
- the KZG10 commit of `ark-poly-commit`
- our own implement of the commit in `zk::commit`

there is also a slight improvement to the previous benchmarking of our `zk::setup`: the degree of the _trusted setup_ is now computed once and for all before the benchmarking loop starts, because it's not what is of interest, let's not benchmark it.