Add timing output to the end of ngen runs

[PhilMiller]

This will allow for slightly more informative benchmark results, in which we can distinguish different elements of the runtime, and extrapolate accordingly.

Changes

• Simplify the mixed MPI/Routing #ifdef logic
• Add time calls and prints

Testing

1. Unit testing still passes

Screenshot

From the CI job running on example data:

Running timestep 700
Finished 720 timesteps.
NGen top-level timings:
	NGen::init: 0.207376
	NGen::simulation: 0.230584
	NGen::routing: 1.232e-06

Todos

• Improve numeric formatting

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Target Environment support

• Linux
• macOS

[PhilMiller]

The refactoring of the ifdef logic was because I wanted to use the same test for printing the timings, and didn't want to make a mess there.

[PhilMiller]

Ugh, and of course in tweaking things between my last local build and pushing, I broke it a bit. That'll be fixed shortly.

[ZacharyWills]

This will greatly help with hardware affinity testing. Ideally we should be able to give some rough numbers about the relationship between domain extent, available hardware, and expected runtime.

Thanks,
Zach

[robertbartel]

I'll leave it to others to formally approve, but I like it overall. Thanks for putting this together @PhilMiller.

[PhilMiller]

Ideally, the textual numeric output would be presented a little more readably, using something like https://github.com/martinmoene/EngFormat-Cpp but that's an inessential refinement, compared to just getting meaningful measurements in place.

All previous comments on the code addressed.

[ZacharyWills]

@PhilMiller
Just for clarity, what units are the timings in?

	NGen::init: 0.207376
	NGen::simulation: 0.230584
	NGen::routing: 1.232e-06

[PhilMiller]

@ZacharyWills Seconds