Make rendering test faster using updated yamatanooroti

[tompng]

Makes test_rendering faster. Yamatanooroti's wait time is reduced from 0.1 sec to 0.01 sec test_yamatanooroti(vterm-yamatanooroti head): 37.58 sec → 10.72 sec

startup_message

We don't need puts 'start IRB'. It does not mean IRB is ready for input. We should check the prompt with startup_message: /irb\(main\)/

close

It does not only close_input but read few bytes and terminates process immediately. Calling close before assert_screen sometimes terminates process before reading the last output.