feat: investigate use of Finalizer to detect/auto-close unclosed bloc instances

## Description

As a developer, it would be helpful to detect if a bloc was not properly closed when it becomes inaccessible to the program. This issue is to investigate the use of [Finalizer](https://master-api.flutter.dev/flutter/dart-core/Finalizer-class.html) within bloc to either detect or prevent blocs from not being properly closed when they are no longer accessible.

## Additional Context

The Finalizer API is available in Dart 2.17 so this would likely not land anytime soon and this is more for exploratory purposes.