Support client-side encryption

### What's the feature are you trying to implement?

Iceberg spec supports client-side encryption and this is largely fully supported in the Java client but we're lagging behind in rust and I think we should change that.

[Iceberg docs](https://iceberg.apache.org/docs/nightly/encryption/)

### Willingness to contribute

I would be willing to contribute to this feature with guidance from the Iceberg Rust community

Start with the Iceberg encryption documentation and compare the existing Java client support with the Rust client. Define the Rust entry points and tests needed to cover client-side encryption, then confirm that the relevant Iceberg encryption behavior is supported and tested.

Written by the indexing model from the issue text.