[Improve][connector-doris] Improved doris source enumerator splits allocation algorithm for subtasks

[JeremyXin]

…location algorithm for subtasks

Purpose of this pull request

Similar to pr #8453, improving doris source enumerator splits allocation algorithm for subtasks and add UT.

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 improves the Doris source enumerator’s splits allocation algorithm for subtasks and adds corresponding unit tests. Key changes include:

• Refactoring the split allocation algorithm to sort splits and assign them using an AtomicInteger.
• Adding unit tests for both file-based and Doris-specific source enumerators.
• Minor formatting corrections in the PartitionDefinition’s toString method.

Reviewed Changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated no comments.

File	Description
seatunnel-translation/seatunnel-translation-base/src/test/java/org/apache/seatunnel/translation/source/ParallelSourceTest.java	Introduces/refactors tests for file source split enumeration and adds tests for Doris source split enumeration.
seatunnel-connectors-v2/connector-doris/src/test/java/org/apache/seatunnel/connectors/doris/split/DorisSourceSplitEnumeratorTest.java	Adds tests validating the Doris source split enumeration and allocation logic.
seatunnel-connectors-v2/connector-doris/src/main/java/org/apache/seatunnel/connectors/doris/source/split/DorisSourceSplitEnumerator.java	Refactors split assignment to use a sorted list and AtomicInteger for load balancing.
seatunnel-connectors-v2/connector-doris/src/main/java/org/apache/seatunnel/connectors/doris/rest/PartitionDefinition.java	Fixes minor formatting in the toString implementation.

Files not reviewed (2)

• pom.xml: Language not supported
• seatunnel-translation/seatunnel-translation-base/pom.xml: Language not supported

Comments suppressed due to low confidence (1)

seatunnel-translation/seatunnel-translation-base/src/test/java/org/apache/seatunnel/translation/source/ParallelSourceTest.java:183

• Consider adding edge-case tests for the allocateFiles method (e.g. when fileSize is less than parallelism) to ensure the allocation logic behaves correctly in these scenarios.

public int allocateFiles(int id, int parallelism, int fileSize) {

[Hisoka-X]

Hi @JeremyXin . Why change this?

[JeremyXin]

@Hisoka-X I wrote this test method for the file connector before. This time, I want to use the Mockito method to optimize this unit test method.

[Hisoka-X]

waiting test case passes.

[Hisoka-X]

Thanks @JeremyXin