This PR adds a `zeta zeta2 predict` subcommand that takes an edit
prediction example markdown file as an argument, and performs zeta2's
prediction, showing the retrieved context and the predicted edit.

* [x] Apply uncommitted diff to get repo into the right state.
* [x] Apply edits in edit history
* [x] Display predicted edits as unified diff, regardless of model
output format

Release Notes:

- N/A

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Co-authored-by: Agus Zubiaga <agus@zed.dev>
Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
Co-authored-by: Ben Kunkle <ben.kunkle@gmail.com>