CPU thermal throttling

[stephane-caron]

Is your proposal related to a problem?

From #87:

Unless very efficiently cooled, modern CPU cannot run at max speed for long. This can considerably skew timings.

Describe the solution you'd like

Make sure the benchmark solves all problem with consistent performance, monitoring and reacting to thermal throttling.

Describe alternatives you've considered

• Monitoring throttling state between solver calls (pro: single thread, con: throttling may happen during a solver call)
• Downscaling to e.g. 50% of the total CPU performance to lower the probability throttling happens

Additional context

See #87.