fix(models): avoid spurious UserWarning on tool-call responses in _build_response_log

[syedjafri06193]

Summary

Fixes #4685.

When the model returns a tool-call (function-call) response, resp.text internally iterates all Part objects and emits a UserWarning for every part that contains a FunctionCall instead of plain text. This warning is unhelpful noise when the caller is just building a debug log string.

• Adds _safe_response_text(resp) before _build_response_log() that extracts text by directly iterating candidates[0].content.parts and joining only part.text values that are not None, bypassing the warning-emitting property entirely.
• Replaces {resp.text} in _build_response_log()'s f-string with {_safe_response_text(resp)}.

Test plan

• Invoke an agent that issues a tool call and confirm no UserWarning: there is no text part appears in logs.
• Confirm text-only responses still produce the correct text in the debug log.
• pytest tests/unittests/models/ passes without new failures.

🤖 Generated with Claude Code

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[adk-bot]

Response from ADK Triaging Agent

Hello @syedjafri06193, thank you for creating this PR!

To help us review your contribution more efficiently, please address the following items from our contribution guidelines:

1. Contributor License Agreement (CLA): The CLA check currently shows a failure. Please visit Google's Contributor License Agreement page to sign or verify your agreement.
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[syedjafri06193]

CLA is signed (Google Individual CLA, Jun 08 2026). Requesting CLA check re-run.

[rohityan]

Hi @syedjafri06193 , Thank you for your contribution! It appears you haven't yet signed the Contributor License Agreement (CLA). Please visit https://cla.developers.google.com/ to complete the signing process. Once the CLA is signed, we'll be able to proceed with the review of your PR. Thank you!

[syedjafri06193]

I have signed it

…

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