fix(mobile): prevent FlashList unmount crash on station change

[sentry]

This PR addresses the IllegalStateException: addViewAt crash occurring on Android in apps/mobile/src/screens/route-list/route-list-screen.tsx.

Root Cause:
The crash was caused by the FlashList being unmounted mid-navigation transition when the [originId, destinationId] effect called setRouteData([]) upon station changes. This led to React Native Fabric attempting to insert a view that was still attached to the outgoing fragment, triggering the addViewAt error. This was a regression, as a previous fix (PR #689) had already addressed this by keeping the list mounted.

Solution:
This fix restores the approach from PR #689:

1. Removed setRouteData([]) from the [originId, destinationId] effect: The FlashList is no longer torn down when stations change, preventing the mid-transition unmount.
2. Introduced routeDataStations state: This state now tracks the { originId, destinationId } for which the current routeData was fetched.
3. Implemented replace-in-place logic in the trains.isSuccess effect: When new data arrives for different stations (detected by comparing with routeDataStations), routeData is now replaced entirely instead of being merged. routeDataStations is updated accordingly.
4. Reset routeDataStations in the [time, hideSlowTrains] effect: Ensures that a full refresh (e.g., changing the date or filter) correctly clears the station tracking.

Fixes BETTER-RAIL-37

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