This PR mostly moves some code around. It also adds a high-level
`format_expected_output` function that routes patch formatting to
specific prompt formats. This was `zeta_prompt` can format
`expected_output` for training.
Keeping everything prompt-related in a "pure" module (with no heavy
dependencies) makes it easier to write bindings.
Release Notes:
- N/A
Oleksiy Syvokon
66ea4b89af