Add nl support and expand rg and git eval coverage

[zac]

Summary

• register BashGit alongside BashPython in BashEvalRunner so local evals exercise optional runtimes
• add a minimal nl command with -ba support for file and stdin input
• fix rg --files to emit relative paths while preserving existing rg search output behavior
• expand BashGit with common non-destructive inspection commands and local git config user.name / user.email persistence
• add parity and coverage tests for the new rg, nl, and git behaviors

Testing

• swift test
• local bashswift eval: .codex-local/evals/codex-real-expanded (25/25)
• local system-bash eval: .codex-local/evals/codex-real-expanded (25/25)
• local bashswift eval: .codex-local/evals/shell-python-local (21/21)