fix(examples) remove cast in MP scripts (#2354)

After https://github.com/lvgl/lv_binding_micropython/pull/161 merged, it is no longer needed to cast the result of 'e.get_target()'

Also, additional small fixes to allow CI improvements

examples/widgets/chart/lv_example_chart_2.py

@@ -1,6 +1,6 @@
 def draw_event_cb(e):
 
-    obj = lv.obj.__cast__(e.get_target())
+    obj = e.get_target()
 
     # Add the faded area before the lines are drawn
     dsc = lv.obj_draw_part_dsc_t.__cast__(e.get_param())

examples/widgets/chart/lv_example_chart_5.py

@@ -44,13 +44,13 @@ ecg_sample = [
 
 def slider_x_event_cb(e):
 
-    slider = lv.slider.__cast__(e.get_target())
+    slider = e.get_target()
     v = slider.get_value()
     chart.set_zoom_x(v)
 
 def slider_y_event_cb(e):
 
-    slider = lv.slider.__cast__(e.get_target())
+    slider = e.get_target()
     v = slider.get_value()
     chart.set_zoom_y(v)
 

examples/widgets/chart/lv_example_chart_6.py

@@ -37,7 +37,7 @@ class ExampleChart_6():
     def event_cb(self,e):
 
         code = e.get_code()
-        chart = lv.chart.__cast__(e.get_target())
+        chart = e.get_target()
 
         if code == lv.EVENT.VALUE_CHANGED:
             # print("last_id: ",self.last_id)