stop method
Implementation
void stop({double? stopAt}) {
if (_state == TweenState.halt) return;
_state = TweenState.halt;
if (stopAt != null) {
t = stopAt;
} else if (_state == TweenState.forwarding) {
t = 1;
} else if (_state == TweenState.backwarding) {
t = 0;
}
}