(iOS) Dynamic pages causes page switch when adding pages at the start

## Environment

Expo v52
React Native 0.76.6
Expo Router v4
iPhone 16 Pro Simulator

## Description

### Summary

I'm using this pager view to show images (similar to iOS photos app), and since there's a lot of images to be loaded, it's images are loaded as requested, similar to FlatList `onStartReached` and `onEndReached`.

### Current behaviour

Adding pages to the end of the data array works very well, but when adding to the start, the current page changes to the new page added based on the page index it was before.

### Expected behaviour

I can see this might be an intended behaviour based on what is being built, but having at least a prop like `preservePage` to update the current page while preserving the page in view (maybe based on page key or id) would be perfect for dynamically loading pages.

I also tested on Android, and it works as expect most of the times, maintaining the correct current page view. Some times it does not update the `activePage` correctly, but the current page view stay as is.

## Findings

On version `6.5.1` of this library, the current page view is preserved as expected, and after digging deeper, I found out that #923 (introduced on `6.6.0`) is the "culprit" for the issue. Although this makes the current page view still visible, the actual `activePage` is not updated accordingly, which also impacts on the position given by `onPageScroll`. It only correctly updates the `activePage` when completing a swipe to the left/right, then `onPageSelected` is called with the correct position.

Inizia riproducendo il comportamento di iOS con pagine anteposte dinamicamente usando la configurazione riportata con Expo v52, React Native 0.76.6 e pager-view 6.6.0. Esamina la modifica introdotta da #923 e confrontala con la versione 6.5.1; quindi verifica che la pagina visibile, activePage e la posizione di onPageScroll rimangano allineati dopo l’aggiunta di pagine all’inizio.

Scritto dal modello di indicizzazione a partire dal testo della issue.