Slight cleanup and refactor of sliderpack

Author: oerc0122

MDANSE_GUI/Src/MDANSE_GUI/Tabs/Plotters/Plotter.py

@@ -17,7 +17,7 @@
 
 import copy
 import enum
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Literal
 
 import numpy as np
 
@@ -87,6 +87,8 @@ def enum_to_str(operation: NormOperations) -> str:
     "operation": NormOperations.AVERAGE,
 }
 
+ValidPlotters = Literal["Grid", "Heatmap", "Single"]
+
 
 class Plotter(metaclass=SubclassFactory):
     """Parent class to all classes used for displaying data."""