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.

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

從 pyiceberg/io/__init__.py 中的 _import_file_io、pyiceberg/table/locations.py 中的 _import_location_provider，以及 pyiceberg/io/pyarrow.py 中的 _import_retry_strategy 開始。追蹤每個屬性如何解析與呼叫，然後確認在實例化之前只接受 FileIO、LocationProvider 或 S3RetryStrategy 的子類別；完成的標準是三個路徑都拒絕無關的可匯入類別。

由索引模型根據 Issue 內容生成。