Signed files keep their signature a string for every YAML parser (#4)

Co-authored-by: Danny Kim <temeddix@gmail.com>
Co-committed-by: Danny Kim <temeddix@gmail.com>

src/sign.rs

@@ -79,6 +79,8 @@ mod tests {
       .map_err(|_| ErrorCode::Internal)?;
     assert!(signed.starts_with("---\ntitle: Notes\n"));
     assert!(signed.ends_with("---\n# Notes\n\nHello\n"));
+    // YAML reads a bare 0x... as an integer, so the signature stays a string.
+    assert!(signed.contains("\nsignature: \"0x"));
     let fields = read_signature(&signed).ok_or(ErrorCode::Internal)?;
     assert_eq!(fields.signer, "laptop.alice.eth");
     let key = parse_key(KEY).ok_or(ErrorCode::Internal)?;