支持Cron表達式、間隔時間的工具（TaskScheduler）

后台任務如何支持間隔時間、Cron表達式兩種方式？
分享一個項目TaskScheduler，這是我從Furion項目中拷出來的

源碼：https://gitee.com/dot-net-core/task-scheduler.git

開始

間隔時間后台服務

    public class IntervalBackgroundService : BackgroundService
    {
        private readonly ILogger<IntervalBackgroundService> _logger = null;
        public IntervalBackgroundService(ILogger<IntervalBackgroundService> logger)
        {
            _logger = logger;
        }
        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                await SpareTime.DoAsync(1000, () =>
                {
                    _logger.LogInformation("Interval Worker running at: {time}", DateTimeOffset.Now);
                }, stoppingToken);
            }
        }
    }

Cron表達式后台服務

    public class CronBackgroundService : BackgroundService
    {
        private readonly ILogger<CronBackgroundService> _logger = null;
        public CronBackgroundService(ILogger<CronBackgroundService> logger)
        {
            _logger = logger;
        }
        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                // 執行 Cron 表達式任務
                await SpareTime.DoAsync("*/5 * * * * *", () =>
                {
                    _logger.LogInformation("Cron Worker running at: {time}", DateTimeOffset.Now);
                }, stoppingToken, CronFormat.IncludeSeconds);
            }
        }
    }