[Subtask] Handle optimistic-lock conflicts in Java and Python clients

### Describe the subtask

After the alter and drop OCC changes are merged, update Java and Python clients to recognize optimistic-lock conflict code 1012, raise a typed OptimisticLockException, and add client-side tests and retry guidance.

### Parent issue

https://github.com/apache/gravitino/issues/12166

Start by reading parent issue #12166 and locating the existing Java and Python client error-handling entry points and client-side test suites. Confirm the alter and drop OCC changes are merged, then use conflict code 1012 as the acceptance case: both clients should expose the typed exception, include tests, and document retry guidance.

Written by the indexing model from the issue text.