feat(io): expose FileIO configuration properties

[smaheshwar-pltr]

What

Add FileIO::properties() and expose configuration from both ArrowS3FileIO and ResolvingFileIO. Other implementations retain an empty default.

Why

Engines that perform their own I/O need the resolved table FileIO configuration, including credentials returned in REST table config. This follows Java FileIO.properties() and PyIceberg's property-map API. Structured storage-credentials remain on SupportsStorageCredentials.

The resolver override is required after the scheme-based FileIO work in apache#828 and apache#889. Because the map may contain credentials, the API contract warns callers not to log or expose it.

Validation

Added S3 and REST resolver coverage, including catalog/table merge precedence. The full GitHub Actions matrix passed.

AI assistance: Codex was used to rebase and adapt the existing change to the current resolver architecture. I reviewed the resulting diff and validation.

[smaheshwar-pltr]

Exposing the FileIO's configuration as a flat map is how other implementations surface it to engines:

• Java FileIO.properties(): https://github.com/apache/iceberg/blob/874e4096e5d16fddbbf43b91f20e248616232cc3/api/src/main/java/org/apache/iceberg/io/FileIO.java#L105
• Rust config().props() (&HashMap): https://github.com/apache/iceberg-rust/blob/47eaef7185916eb86add59d913eb872a06810465/crates/iceberg/src/io/storage/config/mod.rs#L78
• PyIceberg table.io.properties: https://github.com/apache/iceberg-python/blob/01a86f987d1924ca3246a2b985b78890ec0c0fbd/pyiceberg/io/__init__.py#L260-L263
• Trino reads baseTable.io().properties() directly: https://github.com/trinodb/trino/blob/c9a2b907234b94c230cc26e2993411d4afdd77c5/plugin/trino-iceberg/src/main/java/io/trino/plugin/iceberg/catalog/rest/IcebergRestCatalogFileSystemFactory.java#L60