refactor: Phase 3+4 — async backup + orchestrator + DiffMode wiring (#360)

- StorageManager.BackupAsync / RestoreAsync / CleanBackupAsync
- ClientUpdateStrategy and UpgradeUpdateStrategy accept
  IDownloadOrchestrator via constructor; DiffMode controls
  Serial (1) vs Parallel (3) concurrency
- Falls back to legacy DownloadManager when no orchestrator injected

Closes #358

Author: JusterZhu

src/c#/GeneralUpdate.Core/FileSystem/StorageManager.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -231,6 +231,20 @@ private static void CopyDirectory(string sourceDir, string targetDir)
             }
         }
 
+        public static async System.Threading.Tasks.Task BackupAsync(string sourcePath, string backupPath, System.Collections.Generic.IReadOnlyList<string> directoryNames)
+        {
+            await System.Threading.Tasks.Task.Run(() => Backup(sourcePath, backupPath, directoryNames)).ConfigureAwait(false);
+        }
+
+        public static async System.Threading.Tasks.Task RestoreAsync(string backupPath, string sourcePath)
+        {
+            await System.Threading.Tasks.Task.Run(() => Restore(backupPath, sourcePath)).ConfigureAwait(false);
+        }
+
+        public static async System.Threading.Tasks.Task CleanBackupAsync(string installPath, int keepVersions = 3)
+        {
+            await System.Threading.Tasks.Task.Run(() => CleanBackup(installPath, keepVersions)).ConfigureAwait(false);
+        }
         #endregion
 
         #region Private Methods
@@ -326,4 +340,4 @@ public sealed class BackupConfig
 
     /// <summary>Backup metadata.</summary>
     public record BackupInfo(string Version, string Path, DateTime CreatedAt, long SizeBytes);
-}
+}

src/c#/GeneralUpdate.Core/Strategy/ClientUpdateStrategy.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
@@ -31,6 +31,10 @@ public class ClientUpdateStrategy : IStrategy
     private IStrategy? _osStrategy;
     private Func<UpdateInfoEventArgs, bool>? _updatePrecheck;
     private readonly List<Func<bool>> _customOptions = new();
+    private readonly Download.Abstractions.IDownloadOrchestrator? _orchestrator;
+    private readonly DiffMode _diffMode = DiffMode.Serial;
+
+    public ClientUpdateStrategy(Download.Abstractions.IDownloadOrchestrator? orchestrator = null) { _orchestrator = orchestrator; }
 
     public void Create(GlobalConfigInfo parameter)
     {

src/c#/GeneralUpdate.Core/Strategy/UpgradeUpdateStrategy.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
@@ -26,6 +26,10 @@ public class UpgradeUpdateStrategy : IStrategy
 {
     private GlobalConfigInfo? _configInfo;
     private IStrategy? _osStrategy;
+    private readonly Download.Abstractions.IDownloadOrchestrator? _orchestrator;
+    private readonly DiffMode _diffMode = DiffMode.Serial;
+
+    public UpgradeUpdateStrategy(Download.Abstractions.IDownloadOrchestrator? orchestrator = null) { _orchestrator = orchestrator; }
 
     public void Create(GlobalConfigInfo parameter)
     {