Add idempotency support for createTableStaged

### Is your feature request related to a problem? Please describe.

The handler-level idempotency implementation defers idempotency support for the createTableStaged endpoint.
Staged tables are not persisted to the catalog, so the method can safely re-run on retry. The computed location is deterministic (based on namespace location + table name). The only differences on re-run are cosmetic (created-at timestamp and metadata UUID).
Dedicated idempotency support may still be desirable for consistency. Options include skipping idempotency entirely (since re-run is safe) or storing the location in the idempotency record to replay via buildLoadTableResponseWithDelegationCredentials.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start at the createTableStaged endpoint and trace the existing handler-level idempotency implementation, including buildLoadTableResponseWithDelegationCredentials. Decide whether safe reruns are sufficient or whether the idempotency record must retain the deterministic location; done means retries follow the selected behavior without changing the intended response.

Written by the indexing model from the issue text.