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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[syedjafri06193]

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