func (l *Lease) forever() {
	l.expiryMu.Lock()
	defer l.expiryMu.Unlock()
	l.expiry = forever
}
func (l *Lease) forever() {
	l.expiryMu.Lock()
	defer l.expiryMu.Unlock()
	l.expiry = forever
}
// forever sets the expiry of lease to be forever.