Add `SchemaUpdate` logic to Iceberg-Rust

The general philosophy of any engine that implements Iceberg-Rust is that they should not care about things like field-IDs. Therefore we try to hide this logic behind APIs. To allow evolution of the schema, we have the [`UpdateSchema` API in Python](https://github.com/apache/iceberg-python/blob/2ba86b5c852cb0c8f4b4ba95d54fb5a6bfa00fa2/pyiceberg/table/update/schema.py#L74) and the [`SchemaUpdate` (implements `UpdateSchema`) in Java](https://github.com/apache/iceberg/blob/daa24f9c3a56e18d188097deb2dd79cc991c9a78/core/src/main/java/org/apache/iceberg/SchemaUpdate.java#L48). It would be good to have this one in Rust as well :)