Iterate all charts (widgets) when only one overlay

The reason (fsp) subcharts were not linked-updating correctly was
because of the early termination of the interact update loop when only
one "overlay" (aka no other overlays then the main curve) is detected.
Obviously in this case we still need to iterate all linked charts in the
set (presuming the user doesn't disable this).

Also tweaks a few internals:
- rename `start_datums: dict` -> `overlay_table`.
- compact all "single curve" checks to one logic block.
- don't collect curve info into the `overlay_table: dict` when
  `do_overlay_scaling=True`.

piker/ui/_interaction.py

@@ -951,7 +951,7 @@ class ChartView(ViewBox):
 
     def interact_graphics_cycle(
         self,
-        *args,  # capture signal-handler related shit
+        *args,  # capture Qt signal (slot) inputs
 
         debug_print: bool = False,
         do_overlay_scaling: bool = True,
@@ -1017,7 +1017,7 @@ class ChartView(ViewBox):
             # determine auto-ranging input for `._set_yrange()`.
             # this is primarly used for our so called "log-linearized
             # multi-plot" overlay technique.
-            start_datums: dict[
+            overlay_table: dict[
                 ViewBox,
                 tuple[
                     Viz,
@@ -1032,6 +1032,10 @@ class ChartView(ViewBox):
             major_in_view: np.ndarray = None
 
             for name, viz in chart._vizs.items():
+                if debug_print:
+                    print(
+                        f'UX GRAPHICS CYCLE: {viz.name}@{chart_name}'
+                    )
 
                 if not viz.render:
                     # print(f'skipping {flow.name}')
@@ -1087,12 +1091,15 @@ class ChartView(ViewBox):
                     ymn, ymx = yrange
                     # print(f'adding {viz.name} to overlay')
 
+                    if not do_overlay_scaling:
+                        continue
+
                     # determine start datum in view
                     arr = viz.shm.array
                     in_view = arr[read_slc]
                     if not in_view.size:
                         log.warning(f'{viz.name} not in view?')
-                        return
+                        continue
 
                     row_start = arr[read_slc.start - 1]
 
@@ -1103,7 +1110,7 @@ class ChartView(ViewBox):
 
                     profiler(f'{viz.name}@{chart_name} MINOR curve median')
 
-                    start_datums[viz.plot.vb] = (
+                    overlay_table[viz.plot.vb] = (
                         viz,
                         y_start,
                         ymn,
@@ -1152,16 +1159,20 @@ class ChartView(ViewBox):
                         f'{viz.name}@{chart_name} simple std `._set_yrange()`'
                     )
 
-            profiler(f'<{chart_name}>.interact_graphics_cycle({name})')
-            if not start_datums:
-                return
-
-            # if no overlays, set lone chart's yrange and short circuit
+            # NOTE: if no overlay group scaling is wanted by caller, or
+            # there were no overlay charts detected/collected, (could be
+            # either no group detected or chart with a single symbol,
+            # thus a single viz/overlay) then we ONLY set the lone
+            # chart's (viz) yrange and short circuit to the next chart
+            # in the linked charts sequence.
             if (
-                len(start_datums) < 2
-                or not do_overlay_scaling
+                not do_overlay_scaling
+                or len(overlay_table) < 2
+                or not overlay_table
             ):
-                # print(f'ONLY ranging major: {viz.name}')
+                if debug_print:
+                    print(f'ONLY ranging major: {viz.name}')
+
                 if not major_viz:
                     major_viz = viz
 
@@ -1169,7 +1180,9 @@ class ChartView(ViewBox):
                     yrange=yrange,
                 )
                 profiler(f'{viz.name}@{chart_name} single curve yrange')
-                return
+                continue
+
+            profiler(f'<{chart_name}>.interact_graphics_cycle({name})')
 
             # conduct "log-linearized multi-plot" scalings for all groups
             for (
@@ -1183,7 +1196,7 @@ class ChartView(ViewBox):
                     read_slc,
                     minor_in_view,
                 )
-            ) in start_datums.items():
+            ) in overlay_table.items():
 
                 # we use the ymn/mx verbatim from the major curve
                 # (i.e. the curve measured to have the highest