test(firecracker): satisfy pyright on the new infra-VM tests

Two lint fixes, both test-only (no effect on the infra artifact version):
- annotate the TestAdoptable / TestKillInfraFirecrackers helper params
  (reportMissingParameterType).
- test_docker_test_helpers: read __unittest_skip__ via getattr on the
  dynamically-built Case type, matching the sibling assertion — pyright can't
  see the attribute the skip decorator adds (reportAttributeAccessIssue).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A9qa3xoavjQScufDfZaXKR

tests/unit/test_docker_test_helpers.py

@@ -28,7 +28,7 @@ class TestSkipUnlessDockerOrFirecracker(unittest.TestCase):
         ):
             decorated = skip_unless_docker_or_firecracker()(type("Case", (), {}))
 
-        self.assertTrue(decorated.__unittest_skip__)
+        self.assertTrue(getattr(decorated, "__unittest_skip__", False))
 
 
 if __name__ == "__main__":