Implement document loader methods

[pdeziel]

This PR implements the rest of the loader methods for the EnsignLoader.

I have made the following changes:

1. Implement load, lazy_load, and alazy_load
2. Add live tests for live debugging
3. Fix an issue with the gRPC event loop closing and the client not reconnecting

TODOs and questions

Still to do:

• There is an issue with the synchronous methods blocking in a Jupyter environment. I think that something is going on with the async_to_sync method so it's not entirely the fault of this PR, but something we might need to address in a separate issue. The async methods seem to work great in a notebook context so this API is still usuable.

CHECKLIST

• Is the commit message formatted correctly?

• Do all of your functions and methods have docstrings?
• Have you added/updated unit tests where appropriate?
• Have you run the unit tests using pytest?
• Is your code style correct (are you using PEP8, pyflakes)?