suzerain: avoid global comm if possible

The tensor-consistent models, which are exactly the ones expecting
primitive growth rates, don't need RMS fluctuation information.
Don't gather it, saving a smattering of Allreduce traffic.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45126 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: reduce linalg for consistent-models

Rewrite some loopage to avoid memory allocation
as well as avoid linear alegbra on NaNs from the
prior commit.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45127 0bd85f0b-c151-43b9-a1e9-27231104551f