measure atomic operations of curve groups and prime fields (dragoon/komodo!78)

this MR adds two now benchmarks:
- `field_operations` in `benches/operations/field.rs`
- `curve_group_operations` in `benches/operations/curve_group.rs`

as well as `scripts/plot/multi_bar.py` to plot the results, see `benches/README.md` for the commands to run.

## results
![curve_group](/uploads/0a27dcdc7965090b0429867e1822a40c/curve_group.png)

![field](/uploads/461455568a0a637f78f9c2b6d1a68f59/field.png)