lib.App: Add _root_cmd()

Expose __root_cmd (the command which may or may not be mounted at the
root of the subcommand hierarchy) as _root_cmd() to derived classes.
This supports jw-ev's App base class, which specializes it to get hold
of jw.ev.app.Cmd's specific properties.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/App.py

@@ -402,6 +402,9 @@ class App:  # export
     def call_async(self, awaitable: Awaitable[T], timeout: float | None = None) -> T:
         return self.async_runner.call(awaitable, timeout)
 
+    def _root_cmd(self) -> AbstractCmd | None:
+        return self.__root
+
     @property
     def eloop(self) -> asyncio.AbstractEventLoop:
         if self.__eloop is None: