### What problem does this PR solve?

This PR introduces ​**​primitive support for function calls​**​,
enabling the system to handle basic function call capabilities.
However, this feature is currently experimental and ​**​not yet enabled
for general use​**​, as it is only supported by a subset of models,
namely, Qwen and OpenAI models.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)