Function write_baseline_tmpfile 

pub fn write_baseline_tmpfile(
    content: &str,
    file_path: &Path,
) -> Result<NamedTempFile>

Write baseline content to a temporary file with the correct extension.

The extension is preserved so that tree-sitter can detect the language when parsing the temporary file. The caller must keep the returned NamedTempFile handle alive – dropping it deletes the file.