Add notebook demonstrating end-to-end interoperability between third-party agent frameworks and the NeMo Agent toolkit evaluation harness (#1799)

Adds `eval_harbor_atif_interop.ipynb` — a notebook demonstrating end-to-end interoperability between third-party agent frameworks and the NeMo Agent toolkit evaluation harness using ATIF as the interchange format.

The notebook uses real ATIF trajectories generated by [Harbor](https://github.com/harbor-framework/harbor) running `mini-swe-agent` on BFCL (Berkeley Function-Calling Leaderboard) tasks with `nvidia_nim/meta/llama-3.3-70b-instruct`, then evaluates them through `nvidia-nat-eval` using both custom and RAGAS evaluators.

Closes

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## Summary by CodeRabbit

* **New Features**
  * Added a Jupyter notebook demonstrating end-to-end interoperability between Harbor ATIF trajectories and the NeMo evaluation flow, including utilities to extract agent BFCL outputs, two local evaluators (function-call validation and trajectory efficiency), per-sample scoring and detailed reasoning, and an optional LLM-based evaluation path gated by an API key.
* **Documentation**
  * Guided notebook walkthrough covering trajectory loading, sample construction, running evaluators, and comparing Harbor verifier results.

Authors:
  - Yuchen Zhang (https://github.com/yczhang-nv)

Approvers:
  - Anuradha Karuppiah (https://github.com/AnuradhaKaruppiah)

URL: #1799

Author: yczhang-nv