Upgrading flutter_riverpod 2 to 3

ProviderObserver is now marked with base, so external classes can no longer implement it directly.

Removes FamilyNotifier and its variants in favour of Notifier.

Removes all Ref subclasses such as FutureProviderRef; use Ref directly instead.

Removes AsyncValue.valueOrNull; use .value instead.

When an asynchronous provider rebuilds, previous provider subscriptions are removed only when the rebuild completes.

Offline's Storage is now base and requires overriding deleteOutOfDate.

Errors rethrown by ref.watch/ref.read are now wrapped in a ProviderException.

Simplifies parts of the API, such as fusing AutoDisposeNotifier and Notifier.

Moves ChangeNotifierProvider, StateProvider and StateNotifierProvider out of hooks_riverpod.dart to hooks_riverpod/legacy.dart.

All providers now use == to compare previous and new values and filter updates.

Deletes ProviderListenable.addListener, which is now internal-only.

ProviderObserver methods now take a ProviderObserverContext parameter instead of provider and container.

All ref and notifier methods besides mounted now throw if used after disposal.

AsyncValue.value now returns null during errors.

Notifier and variants are now recreated whenever the provider rebuilds, enabling Ref.mounted to check dispose.

StreamProvider now pauses its StreamSubscription when the provider is not actively listened.

Calling ref.watch multiple times now calls ref.onListen every time.

A provider is now considered paused if all of its listeners are also paused.

Makes AsyncValue.copyWithPrevious @internal since it was not meant to be public.

Stops exporting some internal utils.

Adds support for Dart 3.7.0.

Deprecates family.overrideWith in favour of family.overrideWith2, whose callback takes the argument as a parameter.