feature: Tool calling openAI compatible

Did you check the docs?

• I have read all the NeMo-Guardrails docs

Is your feature request related to a problem? Please describe.

The proxy supports OpenAI-compatible tool calls, which allows it to work with the OpenAI SDK. However, for guardrails, it does not accept tool calls in the same format. As a result, I’m forced to choose between using guardrails or tool calls—a trade-off I’d rather avoid.

Describe the solution you'd like

Guardrails chat completions should accept OpenAI-compatible tool calls.

Describe alternatives you've considered

This forces a choice between tool calls and guardrails, neither of which is an option for me.

Additional context

Thank you!