[Improve][Starrocks] Catch lable already exception

[hailin0]

Purpose of this pull request

Does this PR introduce any user-facing change?

How was this patch tested?

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update plugin-mapping.properties and add new connector information in it
  2. Update the pom file of seatunnel-dist
  3. Add ci label in label-scope-conf
  4. Add e2e testcase in seatunnel-e2e
  5. Update connector plugin_config
• Update the release-note.

[Copilot]

Pull Request Overview

This pull request is aimed at improving error handling for duplicate labels in the StarRocks connector by catching and skipping batches when a label reuse is detected.

• Injects a custom StarRocksStreamLoadVisitor via an overloaded constructor to facilitate testing.
• Adds exception handling in flush() to catch an error indicating that a label has already been used.
• Updates the tests to verify that a reused label skips the batch while other errors trigger retries.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
seatunnel-connectors-v2/connector-starrocks/src/main/java/org/apache/seatunnel/connectors/seatunnel/starrocks/client/StarRocksSinkManager.java	Implements error handling for duplicate labels by checking exception messages and breaking out of the retry loop.
seatunnel-connectors-v2/connector-starrocks/src/test/java/org/apache/seatunnel/connectors/seatunnel/starrocks/client/StarRocksSinkManagerTest.java	Adds tests to verify correct handling of duplicate label errors and propagation of other errors with retry behavior.

Comments suppressed due to low confidence (2)

seatunnel-connectors-v2/connector-starrocks/src/main/java/org/apache/seatunnel/connectors/seatunnel/starrocks/client/StarRocksSinkManager.java:102

• Relying on string matching to identify an already-used label exception may be error-prone if exception messages change; consider using a dedicated exception type or error code for a more robust check.

String labelAlreadyMessage = String.format("Label [%s] has already been used", label);

seatunnel-connectors-v2/connector-starrocks/src/test/java/org/apache/seatunnel/connectors/seatunnel/starrocks/client/StarRocksSinkManagerTest.java:73

• [nitpick] Consider renaming the test method to more clearly indicate that it verifies propagation of non-label exceptions (e.g., testNonLabelExceptionPropagation) to improve readability.

void testLabelAlreadyMessageNotHandled() throws Exception {