Use `tn` for nursery vars in UI modules

Rename `root_n` -> `tn` in `_app.py` and
`ln` -> `tn` in `_display.py` to match the `trio` nursery naming
convention used elsewhere. Drop a couple stray blank lines.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/ui/_app.py

@@ -131,11 +131,11 @@ async def _async_main(
 
     async with (
         tractor.trionics.collapse_eg(),
-        trio.open_nursery() as root_n,
+        trio.open_nursery() as tn,
     ):
         # set root nursery and task stack for spawning other charts/feeds
         # that run cached in the bg
-        godwidget._root_n = root_n
+        godwidget._root_n = tn
 
         # setup search widget and focus main chart view at startup
         # search widget is a singleton alongside the godwidget
@@ -165,7 +165,7 @@ async def _async_main(
             # load other providers into search **after**
             # the chart's select cache
             for brokername, mod in needed_brokermods.items():
-                root_n.start_soon(
+                tn.start_soon(
                     load_provider_search,
                     mod,
                     loglevel,

piker/ui/_display.py

@@ -1346,7 +1346,6 @@ async def display_symbol_data(
             fqmes,
             loglevel=loglevel,
             tick_throttle=cycles_per_feed,
-
         ) as feed,
     ):
 
@@ -1461,7 +1460,7 @@ async def display_symbol_data(
 
         async with (
             tractor.trionics.collapse_eg(),
-            trio.open_nursery() as ln,
+            trio.open_nursery() as tn,
         ):
             # if available load volume related built-in display(s)
             vlm_charts: dict[
@@ -1472,7 +1471,7 @@ async def display_symbol_data(
                 flume.has_vlm()
                 and vlm_chart is None
             ):
-                vlm_chart = vlm_charts[fqme] = await ln.start(
+                vlm_chart = vlm_charts[fqme] = await tn.start(
                     open_vlm_displays,
                     rt_linked,
                     flume,
@@ -1480,7 +1479,7 @@ async def display_symbol_data(
 
             # load (user's) FSP set (otherwise known as "indicators")
             # from an input config.
-            ln.start_soon(
+            tn.start_soon(
                 start_fsp_displays,
                 rt_linked,
                 flume,
@@ -1604,11 +1603,11 @@ async def display_symbol_data(
 
             # start update loop task
             dss: dict[str, DisplayState] = {}
-            ln.start_soon(
+            tn.start_soon(
                 partial(
                     graphics_update_loop,
                     dss=dss,
-                    nurse=ln,
+                    nurse=tn,
                     godwidget=godwidget,
                     feed=feed,
                     # min_istream,
@@ -1623,7 +1622,6 @@ async def display_symbol_data(
             order_ctl_fqme: str = fqmes[0]
             mode: OrderMode
             async with (
-
                 open_order_mode(
                     feed,
                     godwidget,