feat(Android, Stack v5): allow for nested container pop via JS

[kkafar]

Description

Previously it has not been possible to pop nested container via JS.
When there was only a single screen left in the JS stack state, the
reducer would deny removing it and would just ignore the operation
printing a warning that pop operation requires at least two screens.

Currently, in such scenario the parent StackContainer (JS component)
will be asked to pop whole screen that hosts the nested container.

Changes

This is achieved by changes in stack container state reducer.
Previously it operated directly on stack, but now I need to somehow
communicate that an action has not been performed directly on the
container and must be forwarded to parent container. We can
not use the parentNavigation directly in the reducer, because:

1. reducer should be pure,
2. we can not dispatch an action directly to the parent container during
   render (and this is when the state reducing takes place), React
   treats it as an error.

Therefore, I see two possibilities here. Either we move all the
StackContainer state to some centralized place (similarly to what
react-navigation does with NavigationContainer) or we stay with
current approach (each StackContainer owns its state) but we emit
this intent as an side effect.

Right now I went with second option. Reducer, when it find it makes
sense, not only updates the stack state, but also produces side effects
to be performed. Currently, there is only single side effect:
PopContainerStackNavigationEffect, but I found it low cost to make it
a bit more generic.

Reducer produces the side effect, which is later consumed by the new
useParentNavigationEffect hook.

Important thing to note in this implementation is the referential
stability of the effects array. The state object id changes every time
state.stack or state.effects change. However, state.effects object
id stays the same as long as there is no change to prevent excessive
rendering.

Given a nested stack, with only a single screen in the nested stack,
the flow is as follows:

1. navigation.pop is dispatched to the nested stack, this triggers
   render.
2. Reducer detects that it has only a single screen & can not perform
   the action, therefore it produces new state with new effects array
   containing the PopContainerStackNavigationEffect.
3. The useParentNavigationEffect schedules the useEffect, which is
   executed after this render.
4. The useEffect is executed triggering render of the outer container
   and consuming the effect (trigger render of the inner container).
5. New render starts from the outer container -> it performs the
   navigation action, detaching the screen that hosts nested container
6. During the same render as in 5., nested container clears its
   state.effects.
7. After the dismiss completes, pop-completed operation is dispatched
   by event listeners & hosting screen & nested container are cleared from
   the state (they no longer render).

Note

Thing to note here, is that the nested stack's only screen, when it's
being dismissed it sends onDismissed(isNativeDismiss=true) event,
because it is dismissed & it's activityMode has never been changed to
detached. I don't think this is causing any problems right now,
but it is definitely something to be aware of.

What happens if there is only a single screen in outer stack & it
hosts the nested stack? Nothing. Renders are triggered, but there is no
one to handle that operation.

Visual documentation

before	after
Screen.Recording.2026-02-03.at.16.35.26.mov	Screen.Recording.2026-02-03.at.16.33.15.mov

Test plan

I'm using TestStackNesting.
Just as the video shows.

Checklist

• Included code example that can be used to test this change.
• Updated / created local changelog entries in relevant test files.
• For visual changes, included screenshots / GIFs / recordings documenting the change.
• For API changes, updated relevant public types.
• Ensured that CI passes (all but Android lint - I'll fix it separately one day)

[t0maboro]

maybe we should be more strict here and use PopContainerStackNavigationEffect ?

[t0maboro]

nit: import type