fix: yield tool_call_parts immediately in live mode to unblock Gemini 3.1 tool calls

[sandeshveerani4]

Summary

Fixes #5407

• Tool call parts received via LiveServerToolCall in GeminiLlmConnection.receive() are now yielded immediately instead of being deferred until turn_complete
• This unblocks function/tool calling for Gemini 3.1 Flash Live models which do not emit turn_complete until they receive the tool response

Problem

Gemini 3.1 Flash Live models send tool calls via LiveServerToolCall and wait for the tool response before sending turn_complete. The current code accumulates tool_call_parts and only yields them on turn_complete or loop exit, creating a deadlock where tools are never executed.

Fix

Yield tool_call_parts immediately after receiving message.tool_call. This is backward-compatible — earlier models that send turn_complete after tool calls will still work because the existing yield paths become no-ops when tool_call_parts is already empty.

Test plan

• Tested with gemini-3.1-flash-live-preview in live mode — tool calls now execute on the first message and the model responds with audio after receiving tool results
• Verified no regression with the existing turn_complete-based flow

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[adk-bot]

Response from ADK Triaging Agent

Hello @sandeshveerani4, thank you for your contribution!

Before we can merge this PR, you will need to sign the Contributor License Agreement (CLA). You can find more information at https://cla.developers.google.com/.

Thanks!

[rohityan]

Hi @sandeshveerani4 ,Thank you for your contribution! We appreciate you taking the time to submit this pull request. Can you please fix the failing unit tests before we can proceed with the review.