base3g/Comms.F90 retains legacy MAPL_CommsMod name — should be renamed to mapl_Comms_mod or deprecated

[tclune]

Background

As part of issue #4958 (rename internal modules to `mapl__mod` convention), `base3g/Comms.F90` and `infrastructure/esmf/comms/MAPL_Comms.F90` both initially resolved to the same module name `mapl_Comms_mod`, causing a collision.

Current State

The two files are not duplicates — they are distinct implementations:

• `base3g/Comms.F90` — large legacy implementation with collective gather/scatter, request types, round-robin PE lists, broadcast variants, etc. Currently retains the old name `MAPL_CommsMod` as a deliberate exception.
• `infrastructure/esmf/comms/MAPL_Comms.F90` — newer, leaner 3G implementation. Has the correct name `mapl_Comms_mod`.

Desired Resolution

`base3g/Comms.F90` should eventually be renamed to `mapl_Comms_mod` (after merging/reconciling with the 3G version) or deprecated and removed entirely as base3g migration completes.

Related

• Rename all internal modules to mapl_<Name>_mod convention #4958 — module rename effort
• Remove base3g symbols from MAPL2 (MAPLBase_mod) after migration complete #4752 — remove base3g symbols from MAPLBase_mod after migration

[atrayano]

Apparently, there are still few calls from base3g/MAPL_Comms.F90 that are still "needed" by the rest of GEOS. Here is the list:

mapl_CommsBcast
mapl_Collective* (Wait, Gather3D, Scatter3D)

MAPL_RoundRobinPEList (needed only in GAAS, we might want to revisit the parallelization strategy there. The existing one uses Arlindo's idea)

MAPL_BcastShared (needed internally by MAPL_LocStream, which we might need to keep during the transition)