Hotfix for grid generation use of mpi operators

[fmalatino]

Description
This PR amends the usage of MPIComm.allreduce in ndsl/grid/generation::MetricTerms._reduce_global_area_minmaxes to use ReductionOperator instances instead of built-in methods.

How Has This Been Tested?
Tested using the tests currently include in the github workflow. An additional test of a numpy backend c12 baroclinic, 1x1 layout run will be added to the pace workflow as well to ensure future commits do not effect model runs.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included

[oelbert]

👍