feat: Add darkmode to ruler

Author: AlejandroFernandezLuces

src/ansys/tools/visualization_interface/backends/pyvista/widgets/ruler.py

@@ -71,14 +71,18 @@ def callback(self, state: bool) -> None:
             self.plotter.remove_actor(self._actor)
             self._actor = None
         else:
+            if self._dark_mode:
+                color = "white"
+            else:
+                color = "black"
             self._actor = self.plotter.show_bounds(
                 grid="front",
                 location="outer",
                 all_edges=False,
                 show_xaxis=True,
                 show_yaxis=True,
                 show_zaxis=True,
-                color="black",
+                color=color,
                 xtitle="X Axis [m]",
                 ytitle="Y Axis [m]",
                 ztitle="Z Axis [m]",