feat(eval): collect Codex token usage

[yzs15]

Summary

• Add --codex-usage-jsonl support for Codex CLI JSONL token usage parsing.
• Persist model_input_tokens and model_output_tokens to runner CSV and runs schema.
• Add evalrun schema/writer tests and TokenUsage metric regression coverage.

Test Plan

• go test -count=1 ./tools/eval/runner ./internal/evalrun
• python -m pytest tests/test_metrics_user_promoted.py
• git diff --check