Avoid ResourceWarning on implicitly closed event pipe sockets

[minrk]

closes spyder-ide/spyder#21017

since there's no 'on thread close event', we need to garbage collect event pipes periodically. I don't love this, and the old code was a lot simpler and closed things always and only when needed, but it's not a great pattern to rely on __del__ to close things, which is why it raises a ResourceWarning.

There will only be something to do when a thread has:

1. triggered an event via print or flush, and
2. closed

so run quite rarely (e.g. 10 seconds)

To see the issue, run:

import warnings
warnings.simplefilter("error", ResourceWarning)
from concurrent.futures import ThreadPoolExecutor

with ThreadPoolExecutor() as pool:
    pool.submit(print, 5)

[blink1073]

Thank you!