Add geography for Tribal Census Tract ACS Estimates

[mariahdaniellecaballero]

Thanks so much for this work. It's really such a central part of my research and teaching, and the updates on it have been excellent. If there's capability down the road, I would love to see the get_acs() function support querying 5-year estimates for Tribal Census Tracts (Homeland, reservation, and off-reservation). While area-based estimates are really useful, I imagine a lot of folks would appreciate understanding the heterogeneity across Tribal lands.

[walkerke]

So, I have long resisted supporting geographies that require a non-standard hierarchy to query them (meaning outside state/county) because of the way I originally wrote the package. The refactor always seemed big.

However, with Claude Code nowadays, nothing is impossible. I will give this some thought!