fix(google): release the genai client when the realtime session closes

[biztex]

Problem

google.realtime.RealtimeSession constructs its own genai.Client (realtime_api.py:488), but aclose() only tears down the websocket and the pending futures — the client is never closed. Its http clients therefore stay alive until the garbage collector reaches them, and both google/genai/client.py:186 and google/genai/_api_client.py:2234 implement __del__ as:

def __del__(self) -> None:
    try:
        asyncio.get_running_loop().create_task(self.aclose())
    except Exception:
        pass

So the close is scheduled as a task on whatever event loop happens to be running when the collector fires — not necessarily the loop the client was created on, and possibly during shutdown.

The visible symptom is in CI: the unit-tests job intermittently fails the fail_on_leaked_tasks check with pending BaseApiClient.aclose / AsyncClient.aclose / httpx AsyncClient.aclose tasks, attributed to whichever test happened to be finishing when the collector ran (I hit it on an unrelated AMD-only PR, #6639).

Fix

RealtimeSession.aclose() now awaits self._client.aio.aclose() after the rest of its teardown, so the session releases what it allocated. Failures there are logged rather than raised, since aclose is a teardown path.

tests/test_plugin_google_realtime.py builds sessions through an async context manager that closes them, instead of leaving them to the collector — otherwise the tests keep leaking clients regardless of the plugin fix. Added a test asserting the close actually reaches the genai client.

Verification

ruff format --check, ruff check, check_types.py (mypy strict) and the full pytest --unit suite all pass locally.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[davidzhao]

lg