I suspect that we are running out of process IDs, or the scheduleris not letting all subprocesses execute, leading to timeouts intests that start subprocesses when other long-running tests areexecuting. This happens often with Python 3.14 tests for some reason.Add a new pytest marker for the tests that start a subprocess attop level, and run these tests in separate runners withoutpytest-xdist parallelization.

- set PYTHONUNBUFFERED=1 to make the subprocess Python unbuffered- set bufsize=0 making the parent process pipe unbuffered- because that can return short reads, check if the subprocess  exited, and if not, yield the CPU- set stdin to DEVNULL and stderr to STDOUT to avoid blocking  related to those