fix: perf instrumentation not available for cpp codspeed

[not-matthias]

Moved from #13, so that it's linked to the correct Linear issue.

Blocked by CodSpeedHQ/instrument-hooks#6

[GuillaumeLagrange]

We also have performance regression introduced on instrumented test, I'm guessing this is due to the instrument-hooks library introduction, could we hunt changes to make them either non existant or as minimal as possible ?

Callgraphs show that we pickup instrumentation in callgrind in a way that we did not before, if we don't change thsi it will be a breaking change: https://codspeed.io/CodSpeedHQ/codspeed-cpp/branches/cod-1040-perf-instrumentation-not-available-for-cpp-codspeed?runnerMode=Instrumentation

[art049]

The regression is quite problematic since it appears to introduce a significant amount of overhead here. For interpreted languages, it doesn't make a big difference, but here, it seems to be substantial for micro benchmarks (even if the ones with regressions are very small). And we'll probably encounter the same issue when we port this to codspeed-rust.

[art049]

Still a few changes left

[not-matthias]

The benchmarks show the correct timings now. We're not optimizing away the memcpy and some benchmarks even have improved performance, since we're placing the measurement_stop closer to the benchmark (so we're not measuring extra instructions)