Extract some of the improvements from to the unified diff prompt from https://github.com/zed-industries/zed/pull/42171 and adds some other about how context work to improve the reliability of predictions. We also now strip the `<|user_cursor|>` marker if it appears in the output rather than failing. Release Notes: - N/A --------- Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>