Selected sparse packs 1

[Yurlungur]

PR Summary

This is another step on the great refactor. Here I just move some dense packs to sparse packs, and in the process move those tasks into the synchronous region of the task list, i.e., they pack over blocks.

This is showing what can be done with #191 now in place. I am doing the migration piece by piece, and so we can merge this in before I (or someone else) moves to doing, e.g., the Riemann solver and reconstruction, which will be the biggest lift.

PR Checklist

• Adds a test for any bugs fixed. Adds tests for new features.
• Format your changes by calling scripts/bash/format.sh.
• Explain what you did.

[brryan]

Looks great

[carlnotsagan]

from my limited knowledge this looks good! only thing i saw was the call to get the coords in par_for in fluid.cpp but im assuming that was intentional. thanks for this improvement, jonah!