propose stress testing for concurrency primitives

[memsharded]

Changelog: Omit Docs: Omit

Checking https://github.com/conan-io/conan/pull/18253, I think that we will need first some minimal "stress" testing of the synchronization primitives (mutex, readers-writers) without any added Conan complexity. Furthermore the wrappers around fasteners in https://github.com/conan-io/conan/pull/18253 seems a bit over-designed, I'd prefer to develop them bottom-up, based on test use cases and needs.

The current PR is only initial proposal of "mutex", but still pending semaphore (readers-writers).