bidi_stream_query documented but not implemented in AdkApp.register_operations()

## Summary

The Google Cloud documentation references `bidi_stream_query` as a supported streaming method for deployed ADK agents on Vertex AI Agent Runtime, but the method does not exist in any public version of the ADK SDK.

## Expected behavior

`bidi_stream_query` should be available as a WebSocket-based bidirectional streaming method on a deployed `AdkApp`, as described in the official discussion post:
https://discuss.google.dev/t/deploy-bidirectional-streaming-agents-with-vertex-ai-agent-engine-and-live-api/266087

## Actual behavior

`AdkApp.register_operations()` returns the following — no `bidi_stream_query`:

```python
{
"": ["get_session", "list_sessions", "create_session", "delete_session"],
"async": ["async_get_session", "async_list_sessions", "async_create_session", "async_delete_session", "async_add_session_to_memory", "async_search_memory"],
"stream": ["stream_query"],
"async_stream": ["async_stream_query", "streaming_agent_run_with_events"],
}
```

Attempting to invoke `bidi_stream_query` on a deployed engine via `client.aio.live.agent_engines.connect()` returns:
```
bidi_stream_query not found. Available methods are: []
```

## Versions tested

- `google-adk==1.32.0` — `bidi_stream_query` absent from `register_operations()`
- `google-adk==2.0.0b1` (beta) — same result, identical `register_operations()` output

Verified locally by importing `AdkApp` and calling `register_operations()` directly:

```python
from vertexai.agent_engines.templates.adk import AdkApp
print(AdkApp.register_operations(None))
# Returns the dict above — no bidi_stream_query
```

## Workaround

Ended up using `streaming_agent_run_with_events` (registered under `async_stream`), which works but:
- Takes a single `request_json: str` parameter (a JSON-serialised `_StreamRunRequest`) rather than a `LiveRequest` object
- Yields `_StreamingRunResponse` dicts rather than ADK `Event` objects directly
- Each yielded chunk is nested as `chunk["output"]["events"]`

Example working call:
```python
request_json = json.dumps({
"message": {"role": "user", "parts": [{"text": message}]},
"user_id": customer_id,
"session_id": session_id,
})
async for chunk in engine.streaming_agent_run_with_events(request_json=request_json):
events = chunk.get("output", chunk).get("events", [])
for event in events:
if event.get("author") == "my_agent":
for part in event.get("content", {}).get("parts", []):
print(part.get("text", ""))
```