This PR closes https://github.com/leanprover/lean4/issues/13770 by
including `Config.zetaUnused` in `Config.toKey`. Without this, two
configs that differ only in `zetaUnused` share a `WHNF`/`isDefEq` cache
key, so reductions performed under one setting can be returned for the
other. The new bit sits at position 22, immediately above `zetaHave`.
🤖 Prepared with Claude Code
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
