Rework Python tests to use pytest, enforce coverage

[kroenlein]

This PR is primarily focused on improving tests on lolopy. It should include no changes to functionality.

Note that coverage is skipped on recursive calls to _make_learners when there are user-defined learners present. It was not clear how to exercise those routes.

• Migrate tests to use pytest, allowing for monkeypatching, and numpy.testing where appropriate
• Rename version.py to version.py, per standard as not a user-facing module
• Combine deploy actions into one script
• Update testing to require 100 % coverage for Python files
• Change __get_state__ in BaseLoloLearner to always copy the state dictionary, as the result returned from latest sklearn uses a tied dictionary, so deleting gateway corrupted the object. Also change the del to a pop so, removing the need for a try / except block.
• Add __init__ to BaseLoloClassifier so that n_classes is not initialized outside of an __init__ method
• Add testing for pickling and migrate testing for json serialization to use a temporary directory
• Migrate file handling from os to pathlib

[mVenetos97]

LGTM