test_silent_stall_still_times_out kept the 0.1s idle window and flaked
once locally under heavy load (load avg ~250): the child was killed
before its single stderr line was read, so the pre-stall-output
assertion saw an empty stderr. Same class as the progress test this PR
de-flakes; give it the same 0.25s budget. The 30s sleep still trips the
window, so the must-time-out direction is unchanged.
teknium1
754a9ef4e7