Function write_generation_hashes 

pub fn write_generation_hashes(
    name: &str,
    hashes: &[(String, String)],
) -> Result<()>

Store generation content hashes: Vec of (path_display, content_hash).

Call this with pre-computed hashes — use hash_content on each file’s content string before calling. Stored before writing to disk so hashes reflect pure codegen output, independent of any on-disk formatter.