pybindgen cannot convert bytestr to string, in _examples/unicode/test.py

```Python
# TODO: need conversion from bytestr to string -- not sure pybindgen can do it?
# bytestr_ret = encoding.HandleString(bytestr)
```

Start with _examples/unicode/test.py and the TODO around bytestr_ret = encoding.HandleString(bytestr). Determine the expected bytestr-to-string behavior and whether the example currently exposes a reproducible failure. Done means the conversion behavior is supported or the limitation is documented with a clear alternative.

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