Replace Boost Timer with std::chrono

[garth-wells]

We've observed accuracy issue with Boost Timer on some systems, plus removing it in favour of std::chrono (https://en.cppreference.com/w/cpp/header/chrono) is one less dependency.

[IgorBaratta]

I think there's also the issue that the timer is stored in seconds.
Maybe this conversion should be left to the end when we report timings.

dolfinx/cpp/dolfinx/common/Timer.cpp

Line 50 in c564469

const double wall = static_cast<double>(elapsed.wall) * 1e-9;

dolfinx/cpp/dolfinx/common/Timer.cpp

Line 43 in c564469

TimeLogManager::logger().register_timing(_task.value(), wall, user, system);

[jpdean]

I checked the boost timer directly (elapsed.wall), and it doesn't seem to be the conversion that's causing the problem. The accuracy of the timer itself seems much worse than std::chrono, but maybe I'm missing something...

[IgorBaratta]

I checked the boost timer directly (elapsed.wall), and it doesn't seem to be the conversion that's causing the problem. The accuracy of the timer itself seems much worse than std::chrono, but maybe I'm missing something...

I mean it more in general. Rounding to seconds with floating-point numbers can lead to accumulated rounding errors when many time values are summed over time. Since we more often measure times in the order micro seconds than days.