Expose config schemas (`TypedDict`) at runtime

I am using Obstore with [Dagster](https://dagster.io/).

Currently, Dagster's config system [does not support forward references](https://github.com/dagster-io/dagster/issues/27975), so Obstore's typed dicts used to annotate configuration options are unusable with Dagster.

I understand this may be just a Dagster problem (I am not sure how easy would it be to support forward references there), but at the same time is there anything preventing Obstore from exposing these objects at runtime instead of just in `.pyi` files? What is the reason for doing things the current way?