Hpc stack build system run scm updates + Grant mods

[grantfirl]

This replaces #311 (rather than add on to it since Dom is out and we need this for the v6 release) and is mostly @climbfuji 's work. @grantfirl 's modifications include:

• merge main into this branch
• update run_scm.py to work with changes found in main and to reinstate the multirun function from file
• fix bug in least common multiple function that was inadvertently modifying argument variables (DOH! -- this led to random runtime failures with certain combinations of n_itt_out and fhswr/fhlwr)
• change default output interval to 6 timesteps instead of 1
• remove references to multi_run_scm.py in CMakeLists.txt
• update rt.sh to use run_scm.py -m instead of multi_run_scm.py

@climbfuji original work includes:

• major updates to CMakeLists.txt to clean up and use hpc-stack exclusively
• remove multi_run_scm.py in favor of run_scm.py with a multirun option (much cleaner and detects failures more reliably)
• update data retrieval scripts
• other cleanup for run_scm.py (particularly log levels, verbosity, elapsed time stuff)

CLOSES #112 CLOSES #278 CLOSES #300 CLOSES #310

[grantfirl]

Looks all good to me. I would have kept the multi-run capability as simple as possible, users who want to run specific combinations of experiments are very likely capable to create their own little bash script with individual SCM runs listed there. But as long as it works, all good.

Good point. It is actually simplified in that if someone only gives the -m option, the supported cases/suite permutations are run, and the only other option is to specify a file that says what needs to be run. There are no options to specify -m and then either a suite or a case via the command line anymore. I guess that there is some more logic in there than absolutely necessary related to file processing because I wanted to provide maximum flexibility. I could get rid of a lot of the logic just be enforcing that the case, suite, and namelist lists are all the same size, but this could lead to a lot of duplication in the multirun setup file.