libuv resamples its internal clock as the floor of the current
monotonic time truncated to whole milliseconds, then schedules a
timer for loop->time + timeout. Since the fractional millisecond
already elapsed at the moment of sampling is discarded, the timer can
fire up to ~1ms before the requested delay has actually passed. This
made asyncio.sleep(n) occasionally return slightly under n, as
reported in MagicStack#739.

Pad the timeout handed to uv_timer_start() by 1ms to compensate, while
leaving the reported deadline (get_when()/TimerHandle.when()) as the
originally requested value.

transport._wait() only waits for the child to be reaped (SIGCHLD), not
for its stdout pipe to be drained and closed. Process exit and pipe EOF
reach libuv through independent kernel mechanisms and can be observed
in different event loop iterations, so the test could assert on
proto.stages before connection_lost had actually fired, sometimes
leaving the pipe/process transports alive past the end of the test.

Wait on the protocol's own connection_lost instead, which uvloop only
fires once the process has exited and all pipes have disconnected.