def _split_substate_key(substate_key: str) -> tuple[str, str]:
    """Split the substate key into token and state name.

    Args:
        substate_key: The substate key.

    Returns:
        Tuple of token and state name.
    """
    token, _, state_name = substate_key.partition("_")
    return token, state_name
Split the substate key into token and state name.

    Args:
        substate_key: The substate key.

    Returns:
        Tuple of token and state name.
    
reflex/state.py