Added a lazy controller in GetBuilder

[omedkane]

Added a lazy controller builder in the props of GetBuilder, so that it can build its controller if need be.

Problem ⚠️:

class MyWidget extends StatelessWidget {
  const MyWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return GetBuilder(
      // this will construct every time the widget rebuils, workaround: prop drill or Get.put()
      // This can be inconvenient if it cost a bit or widget is animated and rebuilt a lot of times
      init: MyGetController(),
      global: true,
      builder: (c) => const Placeholder(),
    );
  }
}

Solution ✅:

class MyWidget extends StatelessWidget {
  const MyWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return GetBuilder(
      // This will construct once
      controllerBuilder: () => MyGetController(),
      global: true,
      builder: (c) => const Placeholder(),
    );
  }
}

Pre-launch Checklist

• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or @jonataslaw said the PR is test-exempt.
• All existing and new tests are passing.