func NewSingleHandler[Req, Resp RoundTripper](h HandlerID, newReq func() Req, newResp func() Resp) *SingleHandler[Req, Resp] {
	s := SingleHandler[Req, Resp]{id: h}
	s.newReq, s.recycleReq = recycleFunc[Req](newReq)
	s.newResp, s.recycleResp = recycleFunc[Resp](newResp)
	if _, ok := any(newReq()).(Recycler); ok {
		s.callReuseReq = true
	}
	return &s
}

// PutResponse will accept a response for reuse.