:bug: Failure with missing conjure_type.__code__

[stheer-pltr]

Release with #142 resulted in below issue. We should check that conjure_type.code exists

File "/Users/stheer/.local/pipx/.cache/bc093e9748e7285/lib/python3.8/site-packages/conjure_python_client/_serde/decoder.py", line 128, in decode_conjure_union_type
    if 'type_of_union' in conjure_type.__code__.co_varnames:
AttributeError: type object '<...>' has no attribute '__code__'