Add benchmark-side Apptainer workspace support

[neubig]

Summary

• add benchmark-side --workspace apptainer support in the shared parser/models and the supported runners
• introduce a reusable create_apptainer_workspace() helper for pre-built agent-server images, with configurable Apptainer runtime env vars
• document Apptainer usage and limitations in the root and benchmark READMEs, plus add focused tests

Testing

• uv run pre-commit run --files README.md benchmarks/utils/args_parser.py benchmarks/utils/models.py benchmarks/utils/image_utils.py benchmarks/gaia/run_infer.py benchmarks/commit0/run_infer.py benchmarks/multiswebench/run_infer.py benchmarks/swebench/run_infer.py benchmarks/swtbench/run_infer.py benchmarks/swebenchmultimodal/run_infer.py benchmarks/swefficiency/run_infer.py benchmarks/openagentsafety/run_infer.py benchmarks/swebench/README.md benchmarks/multiswebench/README.md benchmarks/swefficiency/README.md benchmarks/swebenchmultimodal/README.md tests/test_image_utils.py tests/test_workspace_types.py
• uv run pytest tests/test_image_utils.py tests/test_workspace_types.py

[all-hands-bot]

🟢 Good taste - Clear, honest documentation that solves a real problem.

This accurately reflects the current state: Apptainer is in the SDK but not wired into the benchmark CLI. The writing is pragmatic and gives users concrete paths forward on Docker-restricted systems. No bikeshedding, no pretending features exist that don't - just straightforward technical documentation.

Taste Rating: Elegant
Verdict: ✅ Ship it