[Fix] Support spawn workers in LiveCodeBench evaluation

[tandede]

Motivation

codegen_check_correctness defines its multiprocessing target as a nested function. Process start methods that serialize the target, such as spawn, therefore fail before evaluating any generation with AttributeError: Can't pickle local object. This affects callers that select spawn explicitly and platforms where it is the default.

Modification

• Move the LiveCodeBench subprocess entry point to module scope so it can be serialized by spawn.
• Preserve the existing timeout, memory-limit argument, result, and metadata behavior.
• Keep the existing mock-based memory-limit tests on their required fork context and add a regression test that launches the worker through a real spawn process.

No public API or behavior changes for existing fork users.

Local verification:

• python -m pytest -q tests/openicl tests/prompt --disable-warnings (67 passed, 2 subtests passed)
• python -m pytest -q tests/partitioners tests/summarizers tests/evaluator tests/tasks tests/tools tests/utils --disable-warnings (107 passed, 15 subtests passed)
• python -m pytest -q tests/datasets/test_livecodebench_evaluator.py tests/datasets/test_code_execution.py tests/datasets/test_humaneval.py tests/datasets/test_taco.py --disable-warnings (17 passed, 1 platform-specific skip)
• flake8, isort, yapf, and codespell pre-commit hooks passed for the changed files.

BC-breaking (Optional)

No.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug is added in the unit tests.
• The modification is covered by complete unit tests.
• Documentation is not required because this is an internal portability fix with no public API change.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[tandede]

Hi maintainers, I’m following up on this PR in case it was missed. Both documentation builds have passed, and the LiveCodeBench spawn-worker support fix is ready for review. Please let me know if any changes or additional validation would be helpful. Thank you!