Skill Eval Harness v0.4.2

Changes

• Add skill-benchmark token-overhead for static skill footprint, paired runtime token deltas, objective lift, and lift per 1k extra tokens.
• Document token-overhead usage in README.
• Bump package version to 0.4.2.

Validation

• CI passed on Python 3.10, 3.11, and 3.12.
• Local: python3 -m py_compile *.py examples/adewale-workspace/*.py
• Local: python3 -m unittest discover tests -v
• Local: uv build