优化 不同的数据库，使用不同的 task 线程

Project.SQLiteHelper/SQLiteHelper/SQLiteHelper.cs

@@ -541,8 +541,9 @@ namespace SQLite
             new Task((obj) => {
                 var _sqls = obj as IEnumerable<string>;
                 QueryTran(_sqls);
-            }, queryList).Start(StepByStepTaskScheduler.Current);
+            }, queryList).Start(Scheduler);
         }
+        TaskScheduler Scheduler { get; } = new StepByStepTaskScheduler();
 
         List<string> holdQueryList = new List<string>();
         bool isHoldQueryTran = false;
@@ -945,7 +946,7 @@ namespace SQLite
         public static StepByStepTaskScheduler Instance { get; } = (StepByStepTaskScheduler)Current;
         private readonly BlockingCollection<Task> m_queue = new BlockingCollection<Task>();
 
-        StepByStepTaskScheduler()
+        public StepByStepTaskScheduler()
         {
             //Thread thread = new Thread(Run);
             //thread.IsBackground = true;//设为为后台线程，当主线程结束时线程自动结束