Fix sse streaming function call error with agentops

[areibman]

📥 Pull Request

📘 Description
Addresses a TypeError: can only concatenate str (not "NoneType") to str that occurred during Google ADK streaming with response_modalities=["TEXT"] when a function call was triggered and AgentOps was enabled. The error was caused by attempting to concatenate None values from text parts in the stream. The fix adds explicit None checks in the Google GenAI and Google ADK instrumentation to prevent this.

🧪 Testing
Validated with a new reproducer example (agentops/examples/google_adk/sse_function_call_example.py) that simulates the reported scenario, confirming the TypeError is resolved and streaming with function calls works as expected.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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