Fix: Support tool usage messages with Langfuse OTEL integration

[eycjur]

Support tool usage messages with Langfuse OTEL integration

Langfuse OTEL integration now correctly logs and displays tool calls (function calling) from chat completions.

Relevant issues

Fixes #13764

Pre-Submission checklist

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• I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🐛 Bug Fix

Changes

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