Add type hints to project

It would be great of the python client to add inline type hints, so that e.g. mypy can detect issues

Start with the Python client source and determine the scope of adding inline type hints across the project; the issue names no files or tests. Review how mypy would be run, then define done as the client having type hints that let mypy detect relevant issues without errors from the new annotations.

Written by the indexing model from the issue text.