fix(weave): Allow client to get ref without explicit `weave.init`

[andrewtruong]

This PR allows the client to "get" a ref without explicitly calling weave.init, which is useful in cases where you just want to get an existing table or dataset.

1. We achieve this by temporarily init-ing to de-ref any object if the user has not init;
2. If the graph client is intentionally closed, we just return the ref