feat: Add .widget.UrwidImageScreen

- Add: An urwid screen that clears *kitty* and *iterm2* images at start
  and stop.

src/term_image/widget/__init__.py

@@ -9,7 +9,12 @@
 except ImportError:
     pass
 else:
-    from .urwid import UrwidImage, UrwidImageCanvas, UrwidImageJanitor
+    from .urwid import UrwidImage, UrwidImageCanvas, UrwidImageJanitor, UrwidImageScreen
 
     del urwid
-    __all__ += ["UrwidImage", "UrwidImageCanvas", "UrwidImageJanitor"]
+    __all__ += [
+        "UrwidImage",
+        "UrwidImageCanvas",
+        "UrwidImageJanitor",
+        "UrwidImageScreen",
+    ]

src/term_image/widget/urwid.py

@@ -9,7 +9,7 @@
 import urwid
 
 from ..exceptions import UrwidImageError
-from ..image import BaseImage, ITerm2Image, KittyImage, Size, TextImage
+from ..image import BaseImage, ITerm2Image, KittyImage, Size, TextImage, kitty
 from ..utils import COLOR_RESET_b, ESC_b
 
 # NOTE: Any new "private" attribute of any subclass of an urwid class should be
@@ -601,3 +601,21 @@ def process_shard_tails():
         self._ti_image_cviews = frozenset(images)
 
         return main_canv
+
+
+class UrwidImageScreen(urwid.raw_display.Screen):
+    """A screen that clears all visible :ref:`graphics-based <graphics-based>` images
+    off the screen immediately after it starts and immediately before it stops.
+
+    See the `baseclass
+    <http://urwid.org/reference/display_modules.html#urwid.raw_display.Screen>`_
+    for futher description.
+    """
+
+    def _start(self, *args, **kwargs):
+        super()._start(*args, **kwargs)
+        self.write(kitty.DELETE_ALL_IMAGES)
+
+    def _stop(self):
+        self.write(kitty.DELETE_ALL_IMAGES)
+        super()._stop()