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.

从 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 开始。跟踪每个属性的解析和调用方式，然后验证在实例化之前只接受 FileIO、LocationProvider 或 S3RetryStrategy 的子类；完成的标准是三个路径都拒绝不相关的可导入类。

由索引模型根据 Issue 内容生成。