updateProgress method
Internal method to update progress.
For use by the StreamingText widget only. Reaching 1.0 routes
through _completeOnce so onCompleted fires at most once per cycle
(W25).
Implementation
void updateProgress(double newProgress) {
final clamped = newProgress.clamp(0.0, 1.0);
if (clamped >= 1.0) {
_completeOnce();
return;
}
_progress = clamped;
_notifyProgress();
}