[Catalog] 3rd party game libraries inclusion

PyGambit

Separate this into 3 issues for Gamut, SageMath, OpenSpiel
We want Gamut to be a subset of the catalog
Can also load OpenSpiel/SageMath games with the same names as part of the catalog?
How can we keep external libraries optional dependencies?
Code could be like: pygambit.catalog.load("openspiel_tinyhanabi") which fails if OpenSpiel not installed OR better still; just have the EFGs from OpenSpiel in Gambit Catalog.
- Note: We may need to do a PR to OpenSpiel to ensure the EFG output works for all games, but can make this catalog loader in advance
- Project ideas: https://www.gambit-project.org/gsoc_2026/#idea-8-efgnfg-exporters-for-deepminds-openspiel

OpenSpiel

Update the Gambit catalog such that we can load games from OpenSpiel via one of EFG exporter in python,
Independent EFG exporter in C++ or NFG exporter written in C++, noting that some games will not correctly generate a Gambit EFG or NFG and we should ignore those games for now.

You should be able to load these games via the catalog module like:

pygambit.catalog.load("open_spiel/Atari")

TODO: