test(realtime): verify recovery boundaries and replacement credentials (#3979)

Adds real WebSocket coverage for existing Realtime recovery behavior in
synchronous and asynchronous clients.

- Direct `recv`, no callback, caller abort, nonrecoverable close and
clean close stop without another upgrade.
- Repeated typed admission errors followed by 1011 consume the retry
budget: two retries, three sockets. A successful upgrade alone does not
reset it.
- OpenAI and Azure refresh caller-provided credentials on the
replacement and preserve the connection's path, query, headers and
disabled compression. Azure bearer mode never also sends an API key.
- Cancelling a pending async receive leaves the next event and the
socket usable.

Tests only; no source, signatures, defaults, dependencies or generated
code changed. Uses the existing real server fixture and fake
credentials. The new file applies independently of the in-flight queue
fix (#3978).

Verified 179/179 relevant WebSocket, redirects and send-queue checks on
each of Pydantic 1 and 2; Ruff check/format and git diff pass. Trusted
budget unchanged at 7746/10000.