[bigfooted]

This PR splits off the parmetis improvements from #2931. It turns out that this parmetis improvement is 'almost' always better, and in the worst case performs equally well. It improves MPI performance for cases with inflation layers.

PARMETIS_ANISOTROPY_WEIGHT (default YES) weights the ParMETIS graph edges by cell aspect ratio, gives the edges that chain points into wall-normal lines the largest weight, and moves each line to the rank holding most of its points after partitioning. Lines are then not split between ranks, which keeps the block-Jacobi ILU and line-based agglomeration from seeing fragments of lines.

On stretched boundary-layer meshes this turned stalled or diverging parallel runs into converging ones (2D shear layer, 2D bump, 3D bump, flat plate with multigrid) and made iteration counts match the serial run more closely, with no case that converged without it failing with it. The load imbalance stays within 1.01-1.05 in 2D and up to about 1.3 on a large 3D mesh. The option has no effect on isotropic meshes or without ParMETIS; a warning is printed when it is set explicitly in a build without ParMETIS.

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[bigfooted]

I bumped black up a version and precommit removed a couple of empty lines in some python files.

[bigfooted]

there was also an mpi error in AD that popped up with this PR, it is fixed with 50639a4

[rois1995]

Please address the two code issues described in the inline comments.

[rois1995]

The assessed head (50639a4) has failing parallel primal, parallel adjoint, tutorial, and V&V jobs. Please show that representative changed cases retain convergence and converged physical outputs before refreshing their references. The exact base's numerical suites were skipped after build failures, so I have not established which failures are new.

Please also validate the changed pressure-drop derivative against finite differences at 1, 2, and 4 MPI ranks. The refreshed two-rank reference passes, but an independent comparison is still needed.

Local validation: the MPI normal build passes, and 201-iteration RAE2822 SST/MG runs complete with finite histories in serial and on two ranks with the option enabled and disabled. These short runs do not establish convergence.

[bigfooted]

@rois1995 I fixed the code issues, and now going through the regressions to see if there is anything out of order.