fix: replace geo input assert with ValueError and add test

[dyrpsf]

Description

This PR resolves a lingering todo comment in src/h3/_h3shape.py.

The geo_to_h3shape function contained a debug assertion (assert isinstance(geo, dict) # todo: remove) that was explicitly marked for removal.

To improve robustness, I replaced the raw assertion with a proper ValueError check to prevent confusing TypeError crashes if a user accidentally passes a string. I also added a unit test to test_polyfill.py to ensure this specific bad input is caught correctly.

Maintainers

cc: @dfellis @ajfriend @isaacbrodsky

[dyrpsf]

I noticed the assert in geo_to_h3shape was recently updated to a ValueError on master, but there wasn't a specific test for it. This PR adds a unit test to test_polyfill.py to ensure this ValueError correctly catches invalid string inputs.

[dyrpsf]

I've resolved the merge conflicts and fixed the CI linter error!

Just to recap: it looks like the ValueError fix in _h3shape.py was recently merged into master, so I accepted those incoming changes during the conflict resolution. This PR now strictly adds the missing unit test to test_polyfill.py to ensure that specific ValueError is properly tested against invalid string inputs.

The tests should be completely green now and ready for review!