Add new 'SIMA_TESTDIR' case variable.

[nusbaume]

Tag name (required for release branches):
Originator(s): nusbaume

AI tools used (if applicable; please also add the "AI-generated code" label to the PR):
What: Claude Code Opus 4.8
How: Modified all of the user_nl_cam test files to use the new SIMA_TESTDIR variable.

Description (include the issue title, and the keyword ['closes', 'fixes', 'resolves'] followed by the issue number):

This PR brings in the new SIMA_TESTDIR CIME case variable, which allows for a developer to change the path for all CAM-SIMA physics snapshot test files in a single location, which should make it much easier for any future path changes, or if porting the tests to a new machine.

Fixes #522

Describe any changes made to build system:

M cime_config/config_component.xml

• Added new 'SIMA_TESTDIR' CIME case variable.

Describe any changes made to the namelist: N/A

List any changes to the defaults for the input datasets (e.g. boundary datasets): N/A

List all files eliminated and why: N/A

List all files added and what they do: N/A

List all existing files that have been modified, and describe the changes:
(Helpful git command: git diff --name-status development...<your_branch_name>)

M cime_config/testdefs/testmods_dirs/cam/outfrq_beljaars_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_dme_adjust_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_gw_cam4_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_gw_cam7_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_hack_shallow_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_hb_vdiff_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_held_suarez_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_kessler_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_rk_stratiform_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_rrtmgp_cirrus_gpu/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_rrtmgp_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_rrtmgp_derecho_gpu/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_tj2016_after_coupler_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_tj2016_before_coupler_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_trcdata_bam_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_uw_vdiff_derecho/user_nl_cam
M cime_config/testdefs/testmods_dirs/cam/outfrq_zm_derecho/user_nl_cam

• Modified all physics snapshot 'user_nl_cam' testmod files to use new 'SIMA_TESTDIR' variable.

If there are new failures (compared to the test/existing-test-failures.txt file),
have them OK'd by the gatekeeper, note them here, and add them to the file.
If there are baseline differences, include the test and the reason for the
diff. What is the nature of the change? Roundoff?

derecho/intel/aux_sima:

SMS_Ln9.ne3pg3_ne3pg3_mg37.FKESSLER.derecho_intel.cam-outfrq_se_cslam_multitape (Overall: NLFAIL)
- Known failure

derecho/gnu/aux_sima:

SMS_Ln9.ne3pg3_ne3pg3_mg37.FADIAB.derecho_gnu.cam-outfrq_se_cslam (Overall: DIFF)
- Known failure

derecho/nvhpc/aux_sima (test is run via Github workflow. Only run the test manually if we need to save new baselines):

If this changes climate describe any run(s) done to evaluate the new
climate in enough detail that it(they) could be reproduced:

CAM-SIMA date used for the baseline comparison tests if different than latest:

[jimmielin]

Thanks @nusbaume! Now I have learned how to add variables via CIME too!

[cacraigucar]

I know our testing is just on derecho right now. How does cime handle the different machines? I know I use the same cime variable on derecho and izumi for CAM runs. Should we add a specifier for derecho?