Add ScopedPottery to provide different values to descendants in the tree

[kaboc]

final numPot = Pot.pending<int>();

Pottery(
  pots: {
    numPot: () => 111,
  },
  builder: (context) => HomePage(),
)

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final num1 = numPot(); // 111

    return Scaffold(
      body: ScopedPottery(
        pots: {
          numPot: () => 222,
        },
        builder: (context) {
          final num2 = numPot(); // 111
          final num3 = numPot.of(context); // 222

          return SecondPage();
        }, 
      ),
    );
  }
}

class SecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final num4 = numPot(); // 111
    final num5 = numPot.of(context); // 222

    return Scaffold(
      body: ScopedPottery(
        pots: {
          numPot: () => 333,
        },
        builder: (context) {
          final num6 = numPot(); // 111
          final num7 = numPot.of(context); // 333
          ...
        }, 
      ),
    );
  }
}

It is not possible to dispose of the objects in scoped pots automatically when ScopedPottery is removed from the widget tree because it is unknown which ones are disposable. Although it is possible to automatically call dispose() by checking if the pot is for ChangeNotifier (including ValueNotifier), I want to avoid it as this package is not specifically for ChangeNotifiers. Therefore ScopedPottery should have disposer to enable users to do clean-up manually.