[ENH] Add type hints to active_grids property in grid.py

Added type hints to `active_grids` getter and setter, improving code readability and enabling better type checking. This enhancement ensures consistency in type usage for the `active_grids` property.

Author: Leguark

gempy/core/data/grid.py

@@ -118,11 +118,11 @@ def bounding_box(self):
         return bounding_box_points
 
     @property
-    def active_grids(self):
+    def active_grids(self) -> GridTypes:
         return self._active_grids
 
     @active_grids.setter
-    def active_grids(self, value):
+    def active_grids(self, value: GridTypes):
         self._active_grids = value
         self._update_values()