Allow registry fields with initial_value to not error on not found in input data

[jimmielin]

Tag name (required for release branches):
Originator(s): @jimmielin (with extensive guidance from @peverwhee)

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

• Fixes Setting <initial_value> in registry should allow model to run without reading field from ic file #359

Should enable CAM7 / CAM4 regression tests to run again despite no PBL scheme, if pbuf_pblh includes <initial_value>0.0_kind_phys</initial_value> in registry.xml - separate PR will include this.

Describe any changes made to build system:

• Adds vars_init_value in generation of physics_inputs.F90 to record which variables have an <initial_value> set in registry.xml

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:

A       test/unit/python/sample_files/write_init_files/phys_vars_init_check_initial_value.F90
A       test/unit/python/sample_files/write_init_files/physics_inputs_initial_value.F90
A       test/unit/python/sample_files/write_init_files/simple_reg_initial_value.xml
  - new test sample files for write_init_files

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/cam_autogen.py
M       cime_config/cam_build_cache.py
M       cime_config/cam_config.py
M       src/data/generate_registry_data.py
  - pass variables having initial_value element in registry.xml

M       src/data/write_init_files.py
  - add error_on_not_found=.false. to variables having initial_value element
  - or write info message for variables that cannot be read (i.e., no horizontal dimension)

M       test/unit/python/sample_files/build_cache_files/update_reg_build_cache.xml
M       test/unit/python/test_build_cache.py
M       test/unit/python/test_cam_autogen.py
M       test/unit/python/test_registry.py
M       test/unit/python/test_write_init_files.py
  - fix compatibility of existing tests with new vars_init_value argument
  - add test_simple_initial_value_write_init unit test

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:

derecho/gnu/aux_sima:

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:

[peverwhee]

thanks @jimmielin !

One testing request, but otherwise no notes! Excellent work on the somewhat confusing build cache updates.

[peverwhee]

awesome thanks again @jimmielin

[jimmielin]

After this fix and #362 all regression tests should be able to run even without a PBL scheme.

aux_sima_gnu_20250221115821: 12 tests
  SMS_Ln2.ne5_ne5_mg37.FPHYStest.derecho_gnu.cam-outfrq_hack_shallow_derecho (Overall: DIFF) details:
    FAIL SMS_Ln2.ne5_ne5_mg37.FPHYStest.derecho_gnu.cam-outfrq_hack_shallow_derecho NLCOMP
    FAIL SMS_Ln2.ne5_ne5_mg37.FPHYStest.derecho_gnu.cam-outfrq_hack_shallow_derecho BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu: ERROR BFAIL baseline directory '/glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu/SMS_Ln2.ne5_ne5_mg37.FPHYStest.derecho_gnu.cam-outfrq_hack_shallow_derecho' does not exist
  SMS_Ln9.ne5pg3_ne5pg3_mg37.FCAM4.derecho_gnu.cam-outfrq_se_cslam_analy_ic (Overall: DIFF) details:
    FAIL SMS_Ln9.ne5pg3_ne5pg3_mg37.FCAM4.derecho_gnu.cam-outfrq_se_cslam_analy_ic NLCOMP
    FAIL SMS_Ln9.ne5pg3_ne5pg3_mg37.FCAM4.derecho_gnu.cam-outfrq_se_cslam_analy_ic BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu: ERROR BFAIL baseline directory '/glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu/SMS_Ln9.ne5pg3_ne5pg3_mg37.FCAM4.derecho_gnu.cam-outfrq_se_cslam_analy_ic' does not exist
  SMS_Ln9.ne5pg3_ne5pg3_mg37.FCAM7.derecho_gnu.cam-outfrq_se_cslam_analy_ic (Overall: DIFF) details:
    FAIL SMS_Ln9.ne5pg3_ne5pg3_mg37.FCAM7.derecho_gnu.cam-outfrq_se_cslam_analy_ic BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu: ERROR BFAIL some baseline files were missing