Handle null response output in parser

[lxingy3]

• I understand that this repository is auto-generated and my pull request may not be merged

Changes being requested

Handle response.output = None in parse_response() by treating it the same as an empty output list. This prevents the parser from raising TypeError when a terminal Responses payload has a null output field.

The PR also adds a focused regression test that constructs a completed Response with output=None and verifies parsing returns an empty output list.

Closes #3312.

Additional context & links

Local checks run:

• PYTHONPATH=src python -m pytest tests/lib/responses/test_parse_response.py -q -o addopts=""
• PYTHONPATH=src python -m ruff check src/openai/lib/_parsing/_responses.py tests/lib/responses/test_parse_response.py
• python -m ruff format src/openai/lib/_parsing/_responses.py tests/lib/responses/test_responses.py tests/lib/responses/test_parse_response.py

[marcuswood-oai]

Thank you for the contribution! The null-output parsing and stream recovery fix has landed in #3345, so I am closing this PR as superseded. We appreciate your help!