Function decode_template42_first_message 

pub fn decode_template42_first_message(
    path: &Path,
    width: usize,
    height: usize,
) -> Result<Option<Vec<f32>>, String>

Convenience helper: decode the first template42 message in the file (if any). Returns Ok(Some(Vec)) if a template42 message was found and decoded successfully, Ok(None) if no suitable message was found, or Err on file/IO errors.