Support UGRID Convention for Selafin files

Summary

This issue explores the feasibility of making TELEMAC outputs compliant with the UGRID conventions and the Climate and Forecast (CF) Metadata Conventions, starting directly from the binary format used by TELEMAC.

Why is this feature useful?

Enhancing TELEMAC outputs to follow standardized metadata and mesh conventions—such as UGRID and CF—would increase interoperability with other tools and libraries in the geoscience community.

On xarray-selafin, users have requested support for UGRID-compliant data structures. Leveraging UXARRAY would enable more advanced spatial operations and visualizations of unstructured meshes, making TELEMAC data more accessible and functional within modern Python ecosystems.

How to implement it?

I was wondering if prior work at the binary level can enable CF compliance while maintaining full backward compatibility with current SELAFIN formats. The goal is to establish a shared foundation early on, potentially avoiding duplicated effort across downstream tools and libraries (e.g., in Python, Julia, etc.).