Support continuous batching in sequence batch streaming case

Description

Please read our CONTRIBUTING.md prior to creating your first pull request.

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)

Type of change

Please delete options that are not relevant.

[ ] 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.

 pytest test_example_stateful_sequence_continuous_batching_http.py
============================== test session starts ===============================
platform linux -- Python 3.10.14, pytest-7.3.1, pluggy-1.4.0
rootdir: /home/ubuntu/serve
plugins: cov-4.1.0, mock-3.12.0
collected 3 items

test_example_stateful_sequence_continuous_batching_http.py ...             [100%]

=============================== 3 passed in 19.81s ===============================

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?

pytorch / serve