Swap ClientEngineTests to use TempDir

And also use the correct primitives to wait for state changes. This way
the tests won't deadlock forever in the event of a bug.

src/Tests/Tests.MonoTorrent.Client/MonoTorrent.Client/ClientEngineTests.cs

@@ -36,6 +36,7 @@
 
 using MonoTorrent.Connections;
 using MonoTorrent.Connections.Peer;
+using MonoTorrent.PieceWriter;
 
 using NUnit.Framework;
 
@@ -501,23 +502,21 @@ public async Task SaveRestoreState_OneTorrentFile_NoContainingDirectory ()
         public async Task StartAsyncAlwaysCreatesEmptyFiles ()
         {
             var files = TorrentFile.Create (Constants.BlockSize * 4, 0, 1, 2, 3);
-            using var writer = new TestWriter ();
-            using var rig = TestRig.CreateMultiFile (files, Constants.BlockSize * 4, writer);
+            using var accessor = TempDir.Create ();
+            using var rig = TestRig.CreateMultiFile (files, Constants.BlockSize * 4, new DiskWriter (), baseDirectory: accessor.Path);
 
             for (int i = 0; i < 2; i++) {
-                var downloadingState = rig.Manager.WaitForState (TorrentState.Downloading);
-                var stoppedState = rig.Manager.WaitForState (TorrentState.Stopped);
 
                 await rig.Manager.StartAsync ();
-                Assert.IsTrue (downloadingState.Wait (5000), "Started");
+                Assert.DoesNotThrowAsync (() => rig.Manager.WaitForState (TorrentState.Downloading), "Started");
                 Assert.IsTrue (File.Exists (rig.Manager.Files[0].FullPath));
                 Assert.IsTrue (rig.Manager.Files[0].BitField.AllTrue);
 
                 // Files can be moved after they have been created.
                 await rig.Manager.MoveFileAsync (rig.Manager.Files[0], rig.Manager.Files[0].FullPath + "new_path");
 
                 await rig.Manager.StopAsync ();
-                Assert.IsTrue (stoppedState.Wait (5000), "Stopped");
+                Assert.DoesNotThrowAsync (() => rig.Manager.WaitForState (TorrentState.Stopped), "Stopped");
                 File.Delete (rig.Manager.Files[0].FullPath);
             }
         }