fix: prevent double renders when pushing stacks.

[EvanBacon]

Why

Prevent double renders by cloning state to avoid leaking state between functions.

• fix Expo Router v2 mounting a route twice router#838
• fix Nesting leads to multiple mounts router#733
• fix Multiple re-renders on _layouts and pages. router#320
• The issue Multiple re-renders on _layouts and pages. router#320 has multiple different things linked, but the original case appears to be fixed.
• possibly also addresses Navigation twice on the first screen of a modal (only in production app) router#847

How

• Prevent mutating the input state to avoid invalidating the nested state.

Test Plan

• The testing library doesn't seem to support this case. @marklawlor has been tasked with ensuring the original branch can detect the error https://github.com/expo/expo/compare/%40evanbacon/router/fix-838
  Just in case the testing library isn't fixed, I ran locally with:

• app/_layout.js, app/(a)/_layout.js, app/b/_layout.js

import { Slot } from "expo-router";
export default function RootLayout() {
  return <Slot />
}

• app/(a)/index.js

import { router, useNavigation } from "expo-router";
import {  View } from "react-native";

export default function App() {
  // const navigation = useNavigation();

  setTimeout(() => {
    router.push("/b");
    // navigation.push("b");
  });
  return (
    <View />
  );
}

• app/b/index.js

import { usePathname } from 'expo-router';
import { Text, View } from 'react-native';

let i = 0;
export default function Page() {
  const path = usePathname();
  i++;
  return (
    <View style={{ flex: 1, backgroundColor: i > 1 ? "red" : "white" }}>
      <Text>Path: {path}</Text>
    </View>
  );
}

Checklist

• Documentation is up to date to reflect these changes (eg: https://docs.expo.dev and README.md).
• Conforms with the Documentation Writing Style Guide
• This diff will work correctly for npx expo prebuild & EAS Build (eg: updated a module plugin).