flush method
void
flush()
Implementation
void flush() {
_timer?.cancel();
_timer = null;
if (trailing && (_lastPos != null || _lastNamed != null)) {
_apply(_fn, _lastPos, _lastNamed);
}
_didLead = false;
_lastPos = null;
_lastNamed = null;
_maxTimer?.cancel();
_maxTimer = null;
}