The new film “Challengers” is very steamy, as has been made clear by the trailers featuring Zendaya as a young hotshot tennis player — and later, coach — who is the focal point of a love triangle completed by co-stars Josh O’Connor and Mike Faist. It is playfully dramatic, in the trademark fashion of Italian director Luca Guadagnino (“Call Me by Your Name”). And perhaps most surprisingly, it is actually full of tennis.