[Improvement] Add final to Iceberg table event members, fix return codes for rename and exists operations

[orenccl]

What would you like to be improved?

1. Add final to Iceberg table event members as they should not change after initialization.
2. Based on the Iceberg Open API specification (for rename) and this reference (for exists), the rename and exists operations should return 204 instead of 200.

How should we improve?

1. Add final to Iceberg table-related events and their members, such as IcebergCreateTableEvent.
2. Modify the return codes in IcebergTableOperations and IcebergTableRenameOperations to align with the specification, and update the relevant unit tests.

[orenccl]

@FANNG1
I'm working on this!