Typing issues

This issue will help to track typing issues in Datalab as well as proposals.

Typing errors

SignalObj.get_data() returns a tuple[np.ndarray, np.ndarray] and not a single np.ndarray. The signature of the BaseObj.get_data could be modify to allow type changes for child classes
Many paramclass arguments/attributes are annotated with MyClass instead of type[MyClass]. eg: in ObjectProp.__init__() or BaseProcessor.init_param().
missing types in fitdialogs.py.
cdl.core.model.signal.new_signal_param() argument stype takes a string or None but is compatible with SignalTypes members.
BaseProcessor.compute_10 my return a typing error if parent function is typed to only return a dict of ResultProperties or ResultShape instead of a union of both. Could be fixed by using a Generic bound to both result types. Therefore, the return type of BaseProcessor.compute_10 would be definded by the return type of the function passed into it.
BaseDataPanel.save_to_files() does not have the right typing argument filenames is hinted as str but type not supported inside the method.

Use generics in base classes that are derived into signal and image classes. eg: in BaseActionHandler, the panel attribute should be a generic that is set to SignalProcessor in SignalActionHandler and vice versa in ImageActionHandler. The same principle could be applied in the BaseProcessor and other.