plots: fix reinitialising series

clear() cannot be overridden, which resulted in persistent layout items.
Clearing before removing items in self.series fixes errors of the kind

QGraphicsScene::removeItem: item 0x17a7fb9bb40's scene (0x0) is different from this scene (0x17a7f77e340)

ndscan/plots/plot_widgets.py

@@ -139,11 +139,10 @@ def link_x_axes(self) -> None:
             # also part of it.
             pane.getAxis("bottom").setStyle(showValues=False)
 
-    def clear(self) -> None:
+    def clear_panes(self):
         for pane in self.panes:
             pane.reset_y_axes()
         self.panes.clear()
-        super().clear()
 
 
 class ContextMenuBuilder:

ndscan/plots/rolling_1d.py

@@ -78,10 +78,11 @@ def __init__(self, model: SinglePointModel, get_alternate_plot_names):
         self._history_length = 1024
 
     def _initialise_series(self):
+        self.clear_panes()
+        self.clear()
         for s in self.series:
             s.remove_items()
         self.series.clear()
-        self.clear()
 
         channels = self.model.get_channel_schemata()
         try:

ndscan/plots/xy_1d.py

@@ -192,14 +192,16 @@ def rewritten(points):
 
     def _initialise_series(self, channels):
         # Remove all currently shown items and any extra axes added.
+        self.clear_panes()
+        self.clear()
         for s in self.series:
             s.remove_items()
         self.series.clear()
         self.crosshairs.clear()
         self.unique_x_data.clear()
         self.found_duplicate_x_data = False
         self._clear_annotations()
-        self.clear()
+
         self.subscan_roots = create_subscan_roots(self.selected_point_model)
 
         try: