drop sqlite3 and use .log, optimize some code

lib/providers/client_provider.dart

@@ -231,6 +231,7 @@ class ClientProvider with ChangeNotifier {
 
   /// 挖矿任务变化回调
   void _onMiningTaskChanged(MiningTaskInfo? task) async {
+    final previousTask = _currentMiningTask;
     _currentMiningTask = task;
 
     if (task != null) {
@@ -246,6 +247,10 @@ class ClientProvider with ChangeNotifier {
     } else {
       // 停止挖矿
       await _miningManager.stopMining();
+      // 挖矿任务完成后，从日志中删除该任务
+      if (previousTask != null) {
+        await _database.finishMiningTask(previousTask);
+      }
       
       // 恢复持续挖矿
       await _sustainMiner.resume();