self.batch_update not working / Calling pop_screen multiple times causes a flickering effect / A new method to pop more screens at once

[mzebrak]

I just want to pop a couple of screens (more than one, let's say 2), nothing else.
Now this is a painful experience because there is no public API allowing for that.

It appears to be as simple as:

while not isinstance(self.app.screen, SomeScreen)
    self.app.pop_screen()

but that's not true, because with every pop_screen, there is ScreenResume message being posted which might result in bugs when something depends on that. It also causes old screens to appear for a moment bug I think it's a regression.

I know about the MODES and they can be useful in some scenarios.
But not everything can be generalized to a mode, and even within a given mode, there may be a need to pop several screens.

This is what I do to achieve it and it is still not ideal because of the regression of the flicker effect:

    def pop_screen_until(self, *screens: str | type[Screen[ScreenResultType]]) -> AwaitComplete:
        """
        Pop all screens until one of the given screen is on top of the stack.

        Raises
        ------
        ScreenNotFoundError:  if no screen was found.
        """

        async def _pop_screen_until() -> None:
            for screen in screens:
                if not self._is_screen_in_stack(screen):
                    continue  # Screen not found, try next one

                with self.batch_update():
                    while not self.__screen_eq(self.screen_stack[-1], screen):
                        with self.prevent(ScreenResume):
                            await self.pop_screen()
                    self.screen.post_message(ScreenResume())
                break  # Screen found and located on top of the stack, stop
            else:
                raise ScreenNotFoundError(
                    f"None of the {screens} screens was found in stack.\nScreen stack: {self.screen_stack}"
                )

        return AwaitComplete(_pop_screen_until()).call_next(self)
        
    def _is_screen_in_stack(self, screen_to_check: str | type[Screen[ScreenResultType]]) -> bool:
        return any(self.__screen_eq(screen, screen_to_check) for screen in self.screen_stack)

    def _screen_eq(self, screen: Screen[ScreenResultType], other: str | type[Screen[ScreenResultType]]) -> bool:
        if isinstance(other, str):
            return screen.__class__.__name__ == other
        return isinstance(screen, other)

Also related: #3126 (regression) and #3127

I think it would be really great if:

1. batch_update could respect things like changing screen_stack, changing focus etc. Not only visual changes to the current screen. Consider also such a situation:

    with self.app.batch_update():  # ensure no flicker when taking multiple actions on screens
            await self.app.pop_screen()  # drop current "item" screen
            await self.app.push_screen(Cart())  # we want to go back to this Cart  while being on the  TransactionSummaryFromCart and "escape" binding is pressed
            await self.app.push_screen(TransactionSummaryFromCart())

2. There was some official method allowing for popping multiple screens in a correct way - either something like pop_screen_until(DesiredScreen) or pop_screen(amount=2)

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[willmcgugan]

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