setBot method
Hands playerIndex over to the bot (true) or to a human (false)
— e.g. when a player leaves mid-game.
Implementation
void setBot(int playerIndex, bool isBot) {
RangeError.checkValidIndex(playerIndex, _state.players, 'playerIndex');
final changed = isBot ? _bots.add(playerIndex) : _bots.remove(playerIndex);
if (!changed) return;
_notify();
_scheduleNext();
}