Improve performance and overhead of JoularJX

[adelnoureddine]

Although JoularJX doesn't impact the software it is measuring, the tool itself have non negligible impact on system resources and energy consumption. We want to think of ways to optimize current code, and also for new approach of monitoring that have less overhead.

[adelnoureddine]

I'm closing this issue as many changes and improvements have been done in recent commits and PRs, notably by @JeremyNison. So far, we haven't found noticeable overhead, and the new code and features help in reducing the current low overhead (for instance, by not monitoring power for JoularJX's computation thread).