Investigate use of asyncio-timeout in dev/testing

[ayjayt]

related to #260

Since we support python >=3.8, and because python has very rapidly updated asyncio since then, we are in a weird space where sometimes we use a deprecated library.

We have traditionally used it in testing when building automatically expiring fixtures in conftest, but we may be able to refine kaleido's particular dependencies depending on what tests we do write or plan on writing, or maybe even eliminate it with asyncio's wait_for.

[mmarras]

Is this related?

with (plots / "test.png").open("w", encoding="utf-8") as f:
    f.write(
       fig.to_image(format="png", scale=5)
    )

Task exception was never retrieved
future: <Task finished name='Task-8' coro=<Browser._watchdog() done, defined at c:\Users\XXX(NL)\AppData\Local\miniconda3\envs\datamore\lib\site-packages\choreographer\browser.py:227> exception=TypeError("object int can't be used in 'await' expression")>
Traceback (most recent call last):
File "c:\Users\XXX(NL)\AppData\Local\miniconda3\envs\datamore\lib\site-packages\choreographer\browser.py", line 230, in _watchdog
await self.subprocess.wait()
TypeError: object int can't be used in 'await' expression