_generate_bounds
=======================================================

.. py:function:: petpal.cli.cli_reference_tissue_models._generate_bounds(initial: Union[list, None], lower: Union[list, None], upper: Union[list, None]) -> Union[numpy.ndarray, None]

   Generates the bounds for the fitting parameters.

   This function takes lists of initial fitting parameters, lower bounds, and upper bounds.
   All lists must have the same length. If no initial parameters are provided, the function returns None.

   :param initial: List of initial guesses for fitting parameters. If None, no bounds are generated.
   :type initial: list, optional
   :param lower: List of lower bounds for fitting parameters.
   :type lower: list, optional
   :param upper: List of upper bounds for fitting parameters.
   :type upper: list, optional

   :returns: *(np.ndarray, optional)* -- If initial is not None, then we return a numpy array of shape [n, 3],
             where n is the number of parameters, where column 0 has the initial guesses, column 1 has lower bounds, and
             column 2 has upper bounds. If initial is None, function will return None.

   :raises ValueError: If initial is not None and the length of initial, lower, and upper are not the same.