test that matplotlib event loop integration is responsive

[minrk]

also fixes %matplotlib osx which gets converted to macosx on its way through matplotlib and back

This should hopefully be the regression test for #1458

[minrk]

all the matplotlib tests are passing on mac and windows, need to figure out why linux isn't enabling the event loops

[ccordoba12]

need to figure out why linux isn't enabling the event loops

Perhaps you need to run that test with xvfb?

[minrk]

Perhaps you need to run that test with xvfb?

Probably right, looking at that.

[ianthomas23]

Changes look good to me, and tests pass locally on both macos and linux. I don't understand the CI failures but I assume they are related to xvfb? Matplotlib itself pip installs pytest-xvfb which might be worth a try as with it installed pytest automatically uses xvfb without having to set the PRE_TEST stuff.

[minrk]

with xvfb, the tests are hanging after embed_kernel, which makes me think it might be during setup of test_eventloops

[ianthomas23]

Is it worth just disabling the reliably-failing test_matplotlib_eventloops.py on qt5/python3.14 so we can merge and come back to this later?