chore(metrics): Change output format of metrics

We have improved the format of the benchmarking output. Now the metrics
follow a more standard CSV style.

Example:
```
name,guest,total duration,repeats,average
jolt,fibonacci,1.33,2,0.516
nexus,fibonacci,177.388,2,88.694
risc0,fibonacci,3.828,2,1.914
sp1,fibonacci,13.330,2,6.665
zkm,fibonacci,279.394,2,139.697
zkwasm,fibonacci,106.161,2,53.80
```

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