feat: support criterion 0.8

[xu-cheng]

Update MSRV to 1.86 as it is required by criterion 0.8. Also fixed any clippy issues.

Replace #277.

[tillrohrmann]

I would love if we could get this merged. This will allow us to upgrade our criterion dependency to 0.8 :-)

[vtselfahel]

https://github.com/grafana/pprof-rs seems to be a maintained fork. It may be better to contribute there.

[korniltsev-grafanista]

https://github.com/grafana/pprof-rs seems to be a maintained fork. It may be better to contribute there.

This is a fork we created to address grafana's users problems(bugs, crashes, performance), it is not a general purpose continuation of the pprof-rs.
I would like to keep the number of patches in the fork to the minimum(especially those that do not fix bugs or improve performance). I hope to merge all of our patches to tikv once tikv start to respond. Grafana has no capacity to maintain this rust library as a general purpose continuation.