Make zipDirectory call asynchronous

Added 'await' to the zipDirectory method to ensure the archive creation completes before proceeding. This change improves reliability when creating app archives.

Author: FeodorFitsner

src/serious_python/bin/package_command.dart

@@ -433,7 +433,7 @@ class PackageCommand extends Command {
       stdout.writeln(
           "Creating app archive at ${dest.path} from a temp directory");
       final encoder = ZipFileEncoder();
-      encoder.zipDirectory(tempDir, filename: dest.path);
+      await encoder.zipDirectory(tempDir, filename: dest.path);
 
       // create hash file
       stdout.writeln("Writing app archive hash to ${dest.path}.hash");