Replace boost::mutex/condition_variable with std equivalents #16709

Not sure why boost::condition_variable and boost::mutex have not already been replaced by newer the stand library equivalents. From what I can tell the behaviour should be the same but perhaps I'm missing something subtle or not.

<!--e57a25ab6845829454e8d69fc972939a-->

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

<!--174a7506f384e20aa4161008e828411d-->

Conflicts

Reviewers, this pull request conflicts with the following ones:

• #16539 (wallet: lower -txmaxfee default from 0.1 to 0.01 BTC by Sjors)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

Tests failed due to timeouts, please give them a little nudge.

Restarted failing jobs.

I'm also not aware of differences between boost and std so concept ACK - unless CI failures aren't timeouts but deadlocks or alike.

@promag there is a difference as the timeouts are from the checkqueue_tests.cpp test. I'll run test locally and reopen if I can find a solution.

By itself it should be fine however bench and test need to be updated to use the standard library. The problem with that is the lack of interrupt() in std::thread, both bench and test make use of boost::thread::interrupt() via boost::thread_group::interrupt_all(), which previously would have exited threads waiting in boost::condition_variable::wait().

More work is required for a solution that maintains test and bench compatibility without being cumbersome. If a suitable native solution is created boost::thread_group threadGroup variable in init.cpp could also be replaced as well as some tests.