fix: Incorrect aggregation of KZG benchmark results

[tessico]

Description

commit and open are unaffected much as they don't require precomputation to run the benchmarks. verify needs to first call commit and then open on the same poly, and the bench was calculating the total time to execute the method (i.e. commit + open + verify), not the elapsed time spent only in verify.

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[mrain]

LGTM. Feel free to merge after CI.