refactor: Move CheckpointStore to Service Container

[a-drew]

Summary

Use the container to register concrete CheckpointStores against an interface.

Reasoning

This achieves the same singleton idea as implemented with static::store inside of Checkpoint Model but gives us a more convenient place to put these classes. Binding to the container works really well here as we in fact have an interface and concrete classes that would implement it. The container will let us typehint the store in any needed location and with singleton we can maintain a unique instance for the whole request lifecycle.

Testing

As a refactor, this change should maintain compatibility and keep all existing tests green

[kfriars]

Before even reviewing, I just want to say I ❤️ this idea...

[kfriars]

The only other thing I would consider here, is going one level up by using a facade to resolve the store out of the service container. Saves needing to do the app resolution all the time and you can type hint the methods on the facade.

[a-drew]

The only other thing I would consider here, is going one level up by using a facade to resolve the store out of the service container. Saves needing to do the app resolution all the time and you can type hint the methods on the facade.

I think I can clean our those app() call by adding constructors in Checkpoint and CheckpointObserver and type hinting CheckpointStore as a required parameter 🤔 thoughts?

[a-drew]

turns out models don't offer the type hinting from container magic 😢