spinner method
Returns a spinner frame for the given phase.
Implementation
String spinner(int phase, {SpinnerFrames frames = SpinnerFrames.dots}) {
final list = spinnerFramesList(frames);
final char = list[phase % list.length];
final color = (phase % 2 == 0) ? theme.accent : theme.highlight;
return '${theme.bold}$color$char${theme.reset}';
}