[Fix][Zeta] Adjust the timing of invoking the enumerator open method

[Hisoka-X]

Purpose of this pull request

This PR corrects the confusion of enumerator method calling order on different engines.
In Spark/Flink, we invoke open method before registerReader method.
But in Zeta, we invoke registerReader method before open method.
So this PR correct Zeta bahavior to same as Spark/Flink.

Does this PR introduce any user-facing change?

no

How was this patch tested?

add new test.

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 adjusts when the enumerator's open method is invoked to ensure it is called at the appropriate time during task initialization.

• Move enumerator.open() invocation from the stateProcess method to the init method
• Remove duplicate enumerator.open() call in the READY_START case, ensuring the lifecycle event is still sent

Comments suppressed due to low confidence (1)

seatunnel-engine/seatunnel-engine-server/src/main/java/org/apache/seatunnel/engine/server/task/SourceSplitEnumeratorTask.java:119

• The new placement of enumerator.open() in the init method should be accompanied by additional tests to ensure it integrates correctly with the enumerator's lifecycle.

enumerator.open();