test: fix test_cache_miss and remove unused re import

- test_smolmachines_launch_image: save mock now touches the tarball path
  so tarball.chmod(0o644) doesn't fail with FileNotFoundError
- test_smolmachines_launch (integration): remove unused `re` import
  (pyright reportUnusedImport)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/integration/test_smolmachines_launch.py

@@ -28,7 +28,6 @@ from __future__ import annotations
 
 import os
 import platform
-import re
 import shutil
 import tempfile
 import unittest