Riverpod Mutations Generator

Hello! This is an attempt to cover the gap left behind by the lack of mutation support in riverpod. See rrousselGit/riverpod#1660

Try it out like so!

First, import both this and riverpod_mutations_annotation

dependencies:
  riverpod: ^2.4.4 # Your proffered riverpod package 
  riverpod_annotation: ^2.2.0  
  riverpod_mutations_annotation: ^1.0.0

dev_dependencies:
  build_runner: ^2.3.3
  riverpod_generator: ^2.3.5
  riverpod_mutations_generator: ^1.0.0

@riverpod
class Todo extends _$Todo {
  Future<List<Todo>> build() => fetchTodoList();

  @mutation
  Future<void> addTodo(Todo todo) async {
    await http.post(...., todo.toJson());
  }

  // special @mutationKey allows you to convert a specific parameter into a family key,
  // which you provide ahead of time as you would any family
  // this is useful for tracking multiple instances of the same method
  @mutation
  Future<void> removeTodo({@mutationKey required int id}) async {...}
}

// flutter example
return Consumer(
  builder: (context, ref, child) {
    // normal list of todos
    List<Todo> todos = ref.watch(exampleProvider);
    // here's the fancy part
    AddTodoMutation addTodo = ref.watch(exampleProvider.addTodo);

    // this will allow you to track the same method multiple times, exactly like a family.
    // note: the parameter was removed from `removeTodo()` as shown.
    // This particular value is now stored in the object in `removeTodo.params.id`
    RemoveTodoMutation removeTodo = ref.watch(exampleProvider.removeTodo(id: 4));

    return Row(
      children: [
        AddButton(
          // invoke the Todo.addTodo method
          // disable the button if its currently loading
          onTap: addTodo is AddTodoMutationLoading ? null : () => addTodo(Todo()),
          // show how the side effect is doing
          trailing: switch (addTodo) {
            AddTodoMutationInitial() => Icon(IconData.circle),
            AddTodoMutationLoading() => CircularProgressIndicator(),
            AddTodoMutationSuccess() => Icon(IconData.check),
            AddTodoMutationFailure(:final error) => IconButton(IconData.info, onPressed: () => showErrorDialog(error)),
          },
        ),
        RemoveButton(
          // Notice, the parameter was removed, as it's already stored in the object in `removeTodo.params.id`
          onTap: removeTodo is RemoveTodoMutationLoading ? null : () => removeTodo(),
          // show how the side effect is doing
          trailing: switch (removeTodo) {
            RemoveTodoMutationInitial() => Icon(IconData.circle),
            RemoveTodoMutationLoading() => CircularProgressIndicator(),
            RemoveTodoSuccess() => Icon(IconData.check),
            RemoveTodoFailure(:final error) => IconButton(IconData.info, onPressed: () => showErrorDialog(error)),
          },
        );
      ],
    );
  },
);