Implementation classes named in table properties are imported and instantiated without a type check

Three properties name a class that PyIceberg imports and calls:

| Property | Resolved by | Called as |
|---|---|---|
| `py-io-impl` | `_import_file_io` (`pyiceberg/io/__init__.py`) | `class_(properties)` |
| `write.py-location-provider.impl` | `_import_location_provider` (`pyiceberg/table/locations.py`) | `class_(table_location, table_properties)` |
| `s3.retry-strategy-impl` | `_import_retry_strategy` (`pyiceberg/io/pyarrow.py`) | `class_()` |

Each follows the same pattern:

```python
module = importlib.import_module(module_name)
class_ = getattr(module, class_name)
return class_(...)
```

None of the three checks that the resolved object is the type it is about to be used as — there is no `issubclass` against `FileIO`, `LocationProvider`, or `S3RetryStrategy`. Any importable dotted name resolves and is called, with the property map passed as an argument in two of the three cases.

All three properties are read from the merged table property map, so their values can originate in a table's metadata rather than in the operator's catalog configuration.

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Issue investigation generated via claude, reviewed by Sung, Kevin, Fokko.

Comece com _import_file_io em pyiceberg/io/__init__.py, _import_location_provider em pyiceberg/table/locations.py e _import_retry_strategy em pyiceberg/io/pyarrow.py. Rastreie como cada propriedade é resolvida e invocada e, em seguida, verifique se somente subclasses de FileIO, LocationProvider ou S3RetryStrategy são aceitas antes da instanciação; considera-se concluído quando os três caminhos rejeitarem classes importáveis não relacionadas.

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