Draw last datums on boot

Ensures that a "last datum" graphics object exists so that zooming can
read it using `.x_last()`. Also, disable the linked region stuff for now
since it's totally borked after flipping to the time indexing.

piker/ui/_display.py

@@ -1202,6 +1202,13 @@ async def display_symbol_data(
             # sidepane=False,
             sidepane=godwidget.search,
         )
+
+        # ensure the last datum graphic is generated
+        # for zoom-interaction purposes.
+        hist_chart.get_viz(fqsn).draw_last(
+            array_key=fqsn,
+            only_last_uppx=True,
+        )
         pis.setdefault(fqsn, [None, None])[1] = hist_chart.plotItem
 
         # don't show when not focussed
@@ -1295,6 +1302,13 @@ async def display_symbol_data(
                     last_bar_color=bg_last_bar_color,
                 )
 
+                # ensure the last datum graphic is generated
+                # for zoom-interaction purposes.
+                viz.draw_last(
+                    array_key=fqsn,
+                    only_last_uppx=True,
+                )
+
                 hist_pi.vb.maxmin = partial(
                     hist_chart.maxmin,
                     name=fqsn,
@@ -1406,11 +1420,12 @@ async def display_symbol_data(
                 )
                 godwidget.resize_all()
 
-            await link_views_with_region(
-                rt_chart,
-                hist_chart,
-                flume,
-            )
+            # hist_chart.hide()
+            # await link_views_with_region(
+            #     rt_chart,
+            #     hist_chart,
+            #     flume,
+            # )
 
             # start graphics update loop after receiving first live quote
             ln.start_soon(