Prepare FAIRChem for Hydra 1.4 #2130

Hi! Hydra maintainer here.

Hydra 1.4 is getting closer to release. It is a very large release that catches up on several years of accumulated maintenance debt and contains quite a few breaking changes.

Hydra 1.4 is not ready yet, but projects can try the development release ahead of time to identify compatibility issues and provide feedback before the release is finalized.

One known change affects version_base: values below "1.3" will no longer be accepted. The rationale and migration plan are tracked in Hydra #3237.

FAIRChem currently has three relevant call sites:

• The primary CLI uses version_base="1.1". This is guaranteed to fail during application startup under Hydra 1.4.
• The LAMMPS entry point uses version_base=None.
• The inference benchmark also uses version_base=None.

The primary CLI must be updated to version_base="1.3". All three paths should be tested against Hydra 1.4 because the release contains additional breaking changes beyond version_base.

In addition, fairchem-core declares hydra-core without any version constraints, so Hydra 1.4 will become eligible for installation automatically when released.

I recommend:

• Updating the primary CLI to version_base="1.3".
• Giving the dependency an explicit hydra-core>=1.3 floor.
• Testing all three Hydra paths with the latest development release:

python -m pip install --upgrade --pre hydra-core
pytest tests/core/test_cli.py

The inference benchmark's load_config() helper does not currently have direct test coverage, and the LAMMPS tests do not exercise its Hydra entry point. Adding focused composition and startup tests for those paths would provide coverage for the compatibility check.