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

Lee la discusión en PR 2846 y la implementación de `_init_sigv4` en `pyiceberg/catalog/rest/__init__.py`. Sigue la ruta de `_load_file_io` de REST Catalog y cómo el firmante de S3 está acoplado actualmente a FileIO. Se considera terminado cuando REST Catalog crea el firmante usando su gestor de autenticación y lo pasa a FileIO mediante el override.

Escrito por el modelo de indexación a partir del texto del issue.