fix: omit stream query parameter when stream is None on interactions get

[adi-IL]

Summary

Fixes #2661.

In google/genai/_gaos/google_genai.py, Interactions.get() and AsyncInteractions.get() previously executed stream_bool = bool(_optional_bool(stream, default=False)). This forced stream to boolean False even when omitted or set to None, causing super().get to serialize ?stream=false on all HTTP GET requests.

During backend rollouts, certain endpoints reject unexpected ?stream=false parameters with Unknown name "stream".

Changes

1. Updated Interactions.get() and AsyncInteractions.get() in google/genai/_gaos/google_genai.py to default stream: Any = None and set stream_bool = _optional_bool(stream). When stream is None (the default), stream is omitted from serialized query parameters matching how include_input is handled.
2. Updated and expanded unit tests in google/genai/tests/interactions/test_paths.py to verify that:
   • Default client.interactions.get(id) and client.aio.interactions.get(id) omit ?stream from the request URL.
   • Explicit stream=False serializes ?stream=false.
   • Explicit stream=True serializes ?stream=true.

Testing

Ran pytest suite:

• google/genai/tests/interactions/test_paths.py: 4 passed.
• google/genai/tests/interactions/: 40 passed.