Pull components we rely on from openff-models into gufe

[dotsdl]

It is unlikely that openff-models will have future releases, and none of the OpenFF stack currently depends on it (recently, the small bits openff-interchange were depending on where merged directly in to that library).

Because of this, it makes sense for us to identify the pieces of openff-models gufe currently depends on and migrate those pieces directly into gufe. We can follow this up with simplification where possible.

[IAlibay]

This needs more discussion - it's unclear to me that we want to take the openff-models code instead of the refactor that is now in interchange.