feat: refactor rest signer in fileio

### Feature Request / Improvement

Context: https://github.com/apache/iceberg-python/pull/2846#discussion_r2645920570

Currently S3 signer is tightly coupled with FileIO. This is awkward since the S3 Signer requires interaction with remote service (i.e. REST Catalog) and reuse its auth manager.

We can refactor here and create the signer in REST Catalog and pass to FileIO by overriding its `_load_file_io` function.

Also see [_init_sigv4](https://github.com/apache/iceberg-python/blob/a99dcada431a06329959cb7f71bf961343256bb0/pyiceberg/catalog/rest/__init__.py#L409-L459) for inspiration

阅读 PR 2846 中的讨论，以及 `pyiceberg/catalog/rest/__init__.py` 中 `_init_sigv4` 的实现。跟踪 REST Catalog 的 `_load_file_io` 路径，以及 S3 signer 当前如何与 FileIO 耦合。完成的标准是 REST Catalog 使用其 auth manager 创建 signer，并通过 override 将其传递给 FileIO。

由索引模型根据 Issue 内容生成。