Efficiency improvements for sorting + loading of grid information.

[economon]

Proposed Changes

Give a brief overview of your contribution here in a few sentences.

More efficient loops/maps for sorting of grid points and connectivity during initial reading/partitioning. This is important for very large meshes when running on limited resources.

Due to the changes in the initial ordering of the connectivity, this PR results in minor differences in the residuals for the regressions. They have been updated accordingly.

Related Work

Resolve any issues (bug fix or feature request), note any related PRs, or mention interactions with the work of others, if any.

N/A

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[vdweide]

This all looks good to me. However, in geometry_structure.cpp there are a few places where only the whitespace has changed, see the discussion we had for the feature_hom branch. If you can change that, it is good to go.

[vdweide]

Looks good to me now. If the regression test go through, it can be merged in.