[Docs][Core] Add Javadoc to TaskExecutionService inner classes

[xxzuo]

Fixes: #10546

Purpose of this pull request

This pull request adds comprehensive Javadoc documentation to TaskExecutionService class, which is part of issue #10546 (sub-task of #10533) to add Javadoc to key lifecycle, checkpoint, and multi-table related classes.

The Javadoc improvements include:

1. Class-level Javadoc:

• Expanded description with <ul> lists detailing the service responsibilities
• Added @see references to related internal classes (CooperativeTaskWorker, BlockingWorker, TaskGroupExecutionTracker)

2. Field Javadoc:

• Added documentation for all key fields including hzInstanceName, nodeEngine, classLoaderService, executorService, executionContexts, finishedExecutionContexts, etc.

3. Method Javadoc:

• Added/enhanced Javadoc for public methods: start(), shutdown(), getExecutionContext(), getActiveExecutionContext(), deployTask(), deployLocalTask(), getTask(), cancelTaskGroup(), asyncExecuteFunction(), notifyCleanTaskGroupContext(), reportEvent(), getSeaTunnelConfig(), getServerConnectorPackageClient(), printTaskExecutionRuntimeInfo()
• Added Javadoc for private methods: submitThreadShareTask(), submitBlockingTask(), notifyTaskStatusToMaster()

4. Inner Class Javadoc:

• CooperativeTaskWorker - improved class documentation
• CooperativeTaskWorker.run() - added detailed execution flow with <ol> list
• RunBusWorkSupplier - improved class and method documentation
• BlockingWorker.run() - added detailed execution flow with <ol> list
• TaskGroupExecutionTracker.taskDone() - added completion handling documentation
• TaskGroupExecutionTracker.exception() - added exception recording documentation
• BlockingTaskThreadFactory - added thread naming pattern documentation
• NamedTaskWrapper - added documentation

Does this PR introduce any user-facing change?

No. This is a documentation-only change that adds Javadoc comments to improve code readability and maintainability. No user-facing behavior is changed.

How was this patch tested?

• ./mvnw spotless:apply passed (formatting verified)
• Documentation-only change

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 necessary, please update incompatible-changes.md to describe the incompatibility caused by this PR.
• 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

[Copilot]

Pull request overview

Adds comprehensive Javadoc to TaskExecutionService (SeaTunnel Engine server) to clarify task deployment, lifecycle management, and the cooperative vs. blocking execution model, as part of issue #10546.

Changes:

• Expanded class-level documentation describing responsibilities and execution modes.
• Added/updated Javadoc on key fields and public/private methods.
• Added detailed Javadoc for inner classes involved in cooperative and blocking execution.

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[DanielLeens]

I pulled the diff locally and did not find a blocking issue here.

This stays in the documentation/Javadoc layer, and the added descriptions are aligned with the current execution structure in TaskExecutionService rather than changing behavior. From my side this looks fine to merge.