ParallelCmd class

A command that executes multiple commands in parallel through the Program's command execution system.

Cmd.batch creates a ParallelCmd so that each sub-command's message is forwarded via the runtime's send as soon as it completes. ParallelCmd also delegates special commands like EveryCmd and StreamCmd to Program._executeCommand for proper lifecycle.

Use this when you need to start both regular commands and special commands (like timers or streams) in parallel:

@override
Cmd? init() {
  return ParallelCmd([
    // This EveryCmd will be properly started by Program
    EveryCmd(interval: fps, callback: (t) => TickMsg(t)),
    // This regular command runs alongside
    Cmd.perform(fetchData, onSuccess: DataMsg.new, onError: ErrorMsg.new),
  ]);
}