Cleanup `handle_worker()` in preparation for #2815 (Stop generation early)

[0xfacade]

In this PR, I clean up the handle_worker() method a bit so that I can later extend it (in a future PR). There are no functional changes in this PR.

Changes:

• collect the many variables in a new class HandleWorkerContext that also features methods for initialization and destruction
• collect methods to handle updating the session in new class SessionManager
• move management of futures into a new class FuturesManager
• extract the logic for handling a work request and a worker response from the main loop into their own respective functions

The last change is the most important one for my future changes. In the main loop of handle_worker(), we were already waiting for two different types of futures: newly dequeued work requests from the Redis work queue, and responses from the worker received over the websocket. I'll need to add a third type of future next that allows us to listen to requests to stop generating text (#2815). The results of the different futures used to be differentiated based on their return type, which was very hard to read. I've created a decorator in FuturesManager that wraps the awaitable in another awaitable that returns a tuple, where the first entry is a FutureType enum value, and the second value is the result of awaiting the passed in awaitable. This makes it easy to distinguish what type of result was received.

I tested my changes by spinning up the inference server + worker with docker compose. Then I used the text-client to interface with the server.

Open issues:

• [x] haven't yet been able to run the pre-commit hook - working on it
• [x] need to add more docstrings
• [ ] testing? There don't seem to be any tests

[github-actions[bot]]

:x: pre-commit failed. Please run pre-commit run --all-files locally and commit the changes. Find more information in the repository's CONTRIBUTING.md

[andreaskoepf]

@0xfacade Do you still want to complete work on the todo points (unticked checkboxes) or can it be merged as it is?

[0xfacade]

@olliestanley @andreaskoepf This can be merged! Will work on the extension for the stop generating feature now