TestPaginationControllerExtension<K, T> extension

Extends PaginationController with a test-only factory.

This creates a pre-seeded controller that skips async fetching, making widget tests fast and deterministic.

import 'package:flutter_pagination_pro/testing.dart';

final controller = PaginationController<int, User>.test(
  items: [User('Alice'), User('Bob')],
  status: PaginationStatus.loaded,
  currentPageKey: 1,
);