Unify 2D arrows on the shared painter.

Drop orisys.util.draw_arrows; box live and replay both use
_paint_shared_flow_arrows with sdk_box_policy when no policy is passed.
Recovered box flow uses the same inverse as finger. Verified with
shared/tests/test_image_backend.py arrow/idle/recovered cases.

shared/src/orisys_app_shared/analysis/service.py

@@ -534,9 +534,8 @@ class AnalysisService:
         )
         #: The policy the samples are selected with. Recorded, never keyed (see
         #: ``model.py``): the shipped defaults make a stored result independent of the
-        #: operator's display preferences. A box chain records the live painter's own
-        #: grid; the shared defaults are the finger painter's and would drop every cell
-        #: ``draw_arrows`` still draws.
+        #: operator's display preferences. A box chain records the box sample grid;
+        #: the finger defaults would drop cells that grid still draws.
         if policy is None and chain.sensor_type == "box":
             from orisys_app_shared.acquisition.arrows import sdk_box_policy