jw.pkg.lib.Cmd._run(): Call parent._run()

jw.pkg.lib.Cmd._run() is abstract, but it's nice to give it a default
implementation which calls self.parent._run() in case parent is also
a command class. That allows for some default processing in _run()
for each node up the parent chain.

The children / derived classes just need to make sure all classes in
the hierarchy do:

    async def _run(self, args):
      return await super()._run(args)
      ... add main command logic here ..

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

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

@@ -21,8 +21,10 @@ class Cmd(abc.ABC): # export
         self.__children: list[Cmd] = []
         self.__child_classes: list[type[Cmd]] = []
 
-    async def _run(self, args):
-        pass
+    @abc.abstractmethod
+    async def _run(self, args) -> None:
+        if isinstance(self.__parent, Cmd): # Calling App.run() would loop
+            return await self.__parent._run(args)
 
     def set_parent(self, parent: Any|Cmd):
         self.__parent = parent
@@ -67,10 +69,6 @@ class Cmd(abc.ABC): # export
     async def run(self, args):
         return await self._run(args)
 
-    @abc.abstractmethod
-    async def _run(self, args):
-        pass
-
     def add_subcommands(self, cmds: Cmd|list[Cmds]|Types|list[Types]) -> None:
         if isinstance(cmds, Cmd):
             assert False