Add guidance suggesting using pytest-timeout to handle hangs

[ngoldbaum]

With free-threading and pytest-run-parallel deadlocks and hangs are more likely.

We should suggest using pytest-timeout to avoid this. This will avoid wasting CI resources from hanging jobs and also give projects debugging information. If a timeout is triggered then you will get a faulthandler report, including a full Python traceback. That's usually enough information to identify at least which test is causing a hang. Often under pytest-xdist or the default pytest non-verbose settings it can be very difficult to even determine which test is hanging, so this is a substantial improvement over the default situation.