/// Parses a key-value formatted payload string into individual values.
///
/// The function expects a string in the format:
/// `input=some text;language=python`, and extracts the `input` and `language` fields.
///
/// # Arguments
///
/// * `payload` - A string containing key-value pairs separated by semicolons.
///
/// # Returns
///
/// * A tuple `(input, language)` extracted from the payload. Defaults are empty string and "python" respectively
/// if the keys are not present.