!squash to feat(Pane): Add Pane.split, deprecate Pane.split_window

Author: tony

src/libtmux/pane.py

@@ -759,8 +759,7 @@ def split_window(
             category=DeprecationWarning,
             stacklevel=2,
         )
-        return self.window.split_window(
-            target=self.pane_id,
+        return self.split(
             attach=attach,
             start_directory=start_directory,
             vertical=vertical,