testing; CESM coarse resolution BHIST (for DART)

[kdraeder]

Description of changes

This is one of 5 related (small) PRs are required to implement coarse-resolution BHIST MCC and ERI tests:

1. CESM,
2. ccs_config,
3. cime,
4. components/cmeps,
5. components/mom/MOM6.

I will include their PR numbers after they've all been assigned.

They have been developed under branch names DART_lowres_{component},
which were branched from a CESM clone copied from @alperaltuntas ;
/glade/work/raeder/Models/cesm3_0_alpha08d_mar13

> git describe --tags
  cesm3_0_alpha08d

which implements a coarse-resolution mom via the new testmod mom/tx10deg.
This clone was apparently many commits ahead of cesm3.0_alphabranch,
so many more commits appear in the list of changes, below, than I am contributing.
My only contribution was on Mar 27, 2026.
Did I miss an update step along the way?
I want to preserve the clone in a form in which testing of all of the modified components will work.

Specific notes

Contributors other than yourself, if any:
Guidance and reviews from @jedwards4b @billsacks @alperaltuntas (mom code too) @cacraigucar
@fischer-ncar contributed all of the commits which are not related to mine.

Fixes: [Github issue #s] And brief description of each issue.
I did not open a CESM issue because the work started in other components and spread to CESM.
I'll open one if that helps the workflow.
Otherwise, this PR contributes to fixing encompassing issue ESMCI/cime#4933 and background issue cam ESCOMP/CAM#1482 (closed).
The specific fixes are described in the commit messages.

User interface changes?: [ No/Yes ]
Yes (sometimes). In order to run tests of certain sizes parameters in the new testmod
cime_config/testmods_dirs/allactive/DART_BHIST_lowres
must be set according to instructions in .../README_layout

Testing performed (automated tests and/or manual tests):
The combined code in these 5 PRs passed manual tests:

MCC_cG.ne3pg3_ne3pg3_t232.BHISTC_LT_DART.derecho_intel.allactive-DART_BHIST_lowres--mom-tx10deg
Default NINST (3), and small(_C3 explicit) and medium(_C14 and _C40) tests.
small  = all instances fit on one (develop) node
medium = instances must be spread across >1 (main, cpu) node,
         requiring correct value in MAX_TASKS_PER_NODE
         to prevent an instance from being laid out onto 2 nodes.
large   = each instance gets whole node(s)

ERI.ne3pg3_ne3pg3_t232.BHISTC_LT_DART.derecho_intel.allactive-DART_BHIST_lowres--mom-tx10deg
ERI_cG_C2_P6.ne3pg3_ne3pg3_t232.BHISTC_LT_DART.derecho_intel.drv-fixes4BHISTSWAV--mom-tx10deg
ERI_cG_P6.ne3pg3_ne3pg3_t232.BHISTC_LT_DART.derecho_intel.drv-fixes4BHISTSWAV--mom-tx10deg
drv-fixes4BHISTSWAV was an earlier version of DART_BHIST_lowres.
   It set CLM_BLD_NMLOPTS but not MAX_TASKS_PER_NODE, which was not known to be needed.
   It also set ROF_NCPL, which became unneccessary by the end of development, 
   but did not set GLC_NCPL.
_P6 is spurious; the coarse resolution MOM6 is restricted to 6 tasks.