Tab icon size is hard-coded to 27x27pt with no way to override it

### Summary

Tab icon size is hard-coded to 27×27pt with no way to override it, which makes it impossible to give a single tab item a larger icon.

### Where

Two independent call sites, both fixed:

- [`ios/TabViewProvider.swift:60`](https://github.com/callstack/react-native-bottom-tabs/blob/main/packages/react-native-bottom-tabs/ios/TabViewProvider.swift#L60) — `private var iconSize = CGSize(width: 27, height: 27)`, applied to remotely-loaded icons via `image.resizeImageTo(size: iconSize)`.
- [`ios/TabViewImpl.swift:350`](https://github.com/callstack/react-native-bottom-tabs/blob/main/packages/react-native-bottom-tabs/ios/TabViewImpl.swift#L350) — `let iconSize = CGSize(width: 27, height: 27)` inside `makeTabBarItemImage`, used on the `experimental_bakedTintColors` path.

Because remote images are resized to `iconSize`, supplying a larger source image has no effect.

### Use case

We show the signed-in user's avatar as the Profile tab's icon (a snapshot of our own circular avatar component, handed over as a `file://` PNG). Design wants that avatar rendered noticeably larger than the neighbouring glyph icons, which is a common pattern for a "you" tab — the avatar is a photo of a person rather than a symbol, so it reads better at a larger size, especially with the label hidden via `tabBarLabel: ''`.

At 27pt it is legible but visibly smaller than intended, and there is currently no prop, per-screen option, or `imageInsets`-style escape hatch to change it.

### Proposal

Expose the icon size, ideally per screen so one item can differ from the rest:

```tsx
({ uri: avatarFileUri }),
tabBarIconSize: 34, // new
}}
/>
```

A navigator-level default (`iconSize` on `Tab.Navigator`) with a per-screen override would also work for us. Happy to open a PR if you'd like it in this shape — wanted to check the preferred API first, and whether per-screen sizing raises layout concerns on Android's `BottomNavigationView` that aren't obvious from the iOS side.

### Environment

- `react-native-bottom-tabs` 1.4.0 / `@bottom-tabs/react-navigation` 1.4.0
- React Native 0.85.3, Expo SDK 56, New Architecture, React 19.2.3
- iOS 26.5 simulator (iPhone 17 Pro), Xcode 26.6

Empieza por la React Native tab options API y los dos puntos de llamada de iOS en ios/TabViewProvider.swift:60 y ios/TabViewImpl.swift:350. Comprueba cómo llegarían un navigator-level default y un per-screen override a ambas rutas de tamaño fijo, incluida la cuestión del layout de Android mencionada en la proposal. Se considera terminado cuando la API elegida permite que un tab icon use un tamaño diferente sin romper el comportamiento predeterminado.

Escrito por el modelo de indexación a partir del texto del issue.