fix(rebase): correct test_cached_lookup key and drop duplicate test

Two issues introduced by the rebase conflict resolution:

- test_cached_lookup_requires_ready_marker used _dockerfile_hash as the
  cache-dir key, but cached_agent_rootfs_dir now uses _rootfs_digest (which
  also folds in the guest init). Updated the test to match.
- test_pyproject_toml_change_bumps_version appeared twice in
  test_infra_artifact.py (once from main, once from the PR commit that
  added pyproject.toml support). Removed the duplicate.

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

tests/unit/test_firecracker_image_builder.py

@@ -36,7 +36,7 @@ class TestBuildAgentRootfsDir(unittest.TestCase):
         self.assertEqual(base, out)
 
     def test_cached_lookup_requires_ready_marker(self):
-        digest = image_builder._dockerfile_hash(self.dockerfile)
+        digest = image_builder._rootfs_digest(self.dockerfile)
         base = self.cache / "rootfs" / f"agent-{digest}"
         base.mkdir(parents=True)
         with patch.object(image_builder.util, "cache_dir", return_value=self.cache):