test: verify omitted and explicit Responses WebSocket preconnect (#3968)

The Responses WebSocket preconnect omission fix needs regression
coverage across sync and async clients. Add one test file exercising
both paths against real local WebSocket upgrades, so an absent optional
query field cannot silently turn into an explicit false value. It also
covers false and true when supplied.

The file is tests only, with no production, dependency or generated-code
changes.

Validation on the committed test bytes:
- 319/319 selected Responses and WebSocket tests under Pydantic v2.
- 319/319 under Pydantic v1.
- 2/2 existing live selectors passed.
- Changed-file lint and typing checks passed.