fix: Fix cancelling installation by not prematurely deleting patched APK

[kitadai31]

• Fixes bug: Manager sometimes immediately cancels installation and Export APK button stops working #2224

The issue had been caused by a race condition in asynchronous processing.
In setLastPatchedApp() method, await keyword was needed before deleteLastPatchedApp();

A code to reproduce:

Future<void> deleteLastPatchedApp() async {
  final PatchedApplication? app = getLastPatchedApp();
  if (app != null) {
    print('kitadai31: (2) Starting a 2 seconds wait');
    await Future.delayed(const Duration(seconds: 2)); // <- ADDED
    print('kitadai31: (5) 2 seconds elapsed. Delete files/lastPatchedApp.apk');
    final File file = File(app.patchedFilePath);
    await file.delete();
    await _prefs.remove('lastPatchedApp');
  }
}

Future<void> setLastPatchedApp(PatchedApplication app, File outFile) async {
  print('kitadai31: (1) calling deleteLastPatchedApp()');
  deleteLastPatchedApp();
  final Directory appCache = await getApplicationSupportDirectory();
  print('kitadai31: (3) Starting copying the patched APK to files/lastPatchedApp.apk');
  app.patchedFilePath =
      outFile.copySync('${appCache.path}/lastPatchedApp.apk').path;
  print('kitadai31: (4) Copy succeeded');
  app.fileSize = outFile.lengthSync();
  await _prefs.setString('lastPatchedApp', json.encode(app.toJson()));
}

The code is executed in the order (1) → (2) → (3) → (4) → (5).
As a result, lastPatchedApp.apk is sometimes randomly deleted after copying is succeeded.

Conclusion

The deleteLastPatchedApp() calling in setLastPatchedApp() is unnecessary from the beginning, so this PR removed this.
Because lastPatchedApp.apk and a pref will be overwritten without calling deleteLastPatchedApp().

The calling in reAssessPatchedApps() is also redundant because the file does not exist, so removed.

[kitadai31]

#2332 (fix: Directly save APK to the cache when saving last patched app) can be reflected after this PR just to improve efficiency
but randomization should be reverted

[Kimmon322]

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