clean a jobGroup immediately when it finished

[lxning]

Description

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Please include a summary of the feature or issue being fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes #(issue)

This PR is to address two issues, which caused the delay of releasing jobGroups and threadpool resource, and fix the logical break introduced in #3198

• issue1: not cleanup a jobGroup immediately when its sequence is end.
• issue2: not stop a thread immediately when a jobGroup is in state of "polling a job".

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Feature/Issue validation/testing

Please describe the Unit or Integration tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

• Test

pytest -s test_example_stateful_sequence_continuous_batching_http.py
========================== 3 passed in 89.92s (0:01:29) ==========================

Checklist:

• Did you have fun?
• Have you added tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?