What is the ruling on someone who goes to sleep with the intention of not waking up for prayer, despite outwardly taking measures to wake up for it, and does the ruling differ if the sleep is before or after the prayer time?

It is not permissible to sleep after the time for prayer has begun, except for someone who knows they will wake up and pray within the time. As for wishing not to wake up while taking the means (to do so), we hope that the doer will not be sinful for it, as Allah overlooks inner thoughts, even if this indicates a reluctance towards prayer. A Muslim should love prayer and rejoice in it, and strive to achieve that.