Validates processed simulation settings before execution.
validate_fitting_settings(settings)Invisibly returns TRUE if the settings are valid. Throws an
error with a descriptive message if fit_to is not one of the
accepted options ("Weight", "Consumption", "Ration",
"Ration_prey", "p_value") or if fit_value is not a
positive number. May also emit warnings for biologically unusual values
(e.g. very low target weight, or a p_value greater than 5).
Processed simulation settings. Must be a list containing at
least the elements fit_to (character) and fit_value
(positive numeric).