Update run_script_in_play_mode description, Fix the issue if enter play multiple times by start_stop_play.

[ShiqiAi]

StudioTestService:ExecutePlayModeAsync({}) may error "Previous call to start play session has not been completed" immediately(still yielding) or yield until stop.

We want to return error message if it errors, or return success without waiting for the function return.
since it is yielding calls in both returns, we can not check it by something like if coroutine.status(co) == "suspended" then

Use function call with timeout instead