Move to Mutex & Condition from Domain.Sync.{notify/wait}

[ctk21]

This PR is an update of #17. It uses the Mutex and Condition module as introduced by ocaml-multicore#548.

I got the following sandmark results (detuned machine but using chrt -1 and taskset) for speedup:

and execution time:

[ctk21]

I have rerun our larger tests on a bigger machine (upto 128 domains):

These tests should be compared with our earlier work here: ocaml-multicore/ocaml-multicore#387 (comment)

Broad brush these results are inline with our 2020-Sep results on the 4.10 based multicore. There are some cases at higher core count where the existing Domain.Sync.{wait,notify} is outperforming mutex/condvar.

[kayceesrk]

Lgtm. I compared this PR with the earlier implementation here. It appears the same except for the Condition.broadcast instead of Condition.signal fixing the bug discovered by #25.

[Sudha247]

This one looks good to go. Thanks for the work @ctk21 & @kayceesrk! Merging.