Simplify JEDI shared bias input staging

[Copilot]

Description

Bias input staging in ush/python/pygfs/jedi/jedi.py was still routing through bias_files_dict even though every supported observation resolved to the same archive, varbc_params.tar. This change makes the shared-archive behavior explicit in stage_obsbiasin() and leaves save_obsbiasout() unchanged.

• Bias input staging

  • Stage a single shared archive, varbc_params.tar, when observations is non-empty.
  • Stop using per-observation bias_files_dict lookups in this module.
  • Preserve current skip behavior when the archive is missing by warning and continuing.

• Behavior preserved

  • Duplicate observations no longer affect staging; the shared archive is copied and extracted once.
  • Bias output archival still tars whatever bias files already exist.

• Regression coverage

  • Add focused unit coverage for:
    • staging the shared archive once with duplicate observations
    • warning and skipping cleanly when the shared archive is absent

bias_tarball = self.jcb_config[f'{self.component}_obsbiasin_prefix'] + 'varbc_params.tar'
if self.jcb_config['observations']:
    bias_src = os.path.join(comin, bias_tarball)

Type of change

• Bug fix (fixes something broken)
• New feature (adds functionality)
• Maintenance (code refactor, clean-up, new CI test, etc.)

Change characteristics

• Is this change expected to change outputs (e.g. value changes to existing outputs, new files stored in COM, files removed from COM, filename changes, additions/subtractions to archives)? NO
  • GFS
  • GEFS
  • SFS
  • GCAFS
• Is this a breaking change (a change in existing functionality)? NO
• Does this change require a documentation update? NO
• Does this change require an update to any of the following submodules? NO
  • EMC verif-global
  • GDAS
  • GFS-utils
  • GSI
  • GSI-monitor
  • GSI-utils
  • UFS-utils
  • UFS-weather-model
  • wxflow

How has this been tested?

• Added targeted unit coverage in dev/ci/scripts/unittests/test_jedi_bias_staging.py for shared-archive staging, duplicate observations, and missing-archive warnings.

Checklist

• Any dependent changes have been merged and published
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have documented my code, including function, input, and output descriptions
• My changes generate no new warnings
• New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added
• Any new scripts have been added to the .github/CODEOWNERS file with owners
• I have made corresponding changes to the system documentation if necessary