Introduce ClientStates enumeration

[stankudrow]

Resolving the relevant FIXME in the nats/aio/client.py module.

The client states are made public (out of the Client class), but not in a separate module (so be it for now). Also the code was formatted with the ruff tool.

Finally the pytest.ini section is appended into the pyproject.toml file.

[stankudrow]

@caspervonb , hello, could you possibly have a look at the PR?

[caspervonb]

I've seen it, will review properly on Monday. Sorry caught a stomach bug mid week.

[stankudrow]

Oh, I wish you a speedy and an easy recovery, hope you'll get well as soon as possible.

[stankudrow]

@caspervonb , rebased, there are problems, e.g., https://app.travis-ci.com/github/nats-io/nats.py/jobs/627146027 and https://app.travis-ci.com/github/nats-io/nats.py/jobs/627146023 from the details.

[stankudrow]

Hm, did this test become flaky? https://app.travis-ci.com/github/nats-io/nats.py/jobs/627155945 - I ain't wanna fix it in this PR, just pointing it out.

[caspervonb]

Core change is probably okay with me but, there's quite a bit of noise added to it.

[stankudrow]

@caspervonb , @wallyqs

[stankudrow]

@wallyqs , @caspervonb , could you approve this PR if you are fine with changes?

And which contributors can I ping here as well?

[stankudrow]

@caspervonb , @wallyqs

[stankudrow]

@wallyqs , @caspervonb , sorry, but pinging.

[Jarema]

We will take a look at this shortly.

[stankudrow]

@Jarema , can this PR be reviewed? It requires no rebase for now and some requests were addressed.