This PR improves Zeta2's matching of `old_text`/`new_text` pairs, using similar code to what we use in the edit agent. For right now, we've duplicated the code, as opposed to trying to generalize it. Release Notes: - N/A --------- Co-authored-by: Max <max@zed.dev> Co-authored-by: Michael <michael@zed.dev> Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com> Co-authored-by: Agus <agus@zed.dev>