Auto-stubbing missing imports: restrict stubs to the target package's importers

To run one code path of a library with huge infra deps (MQTT, cloud SDKs, trackers) without installing them, a sys.meta_path finder that returns MagicMock modules for any missing top-level package works, but it breaks torch and sympy. They probe optional packages (triton, flint/gmpy2) and must get ImportError; with MagicMocks you get errors like 'AssertionError: Unhandled config tlx_mode=<MagicMock ...>' or 'ValueError: not enough values to unpack' in sympy's gmpy check. Fix: in find_spec, walk sys._getframe() past importlib frames and stub only when the importing frame's __name__ starts with the target package. Also print the list of stubbed modules, so a reviewer can see that none lies on the code path you are testing.