Summary

This PR prevents undefined HexGrid configurations by disallowing toroidal grids with odd dimensions, which previously resulted in asymmetric neighbor wiring.

Bug / Issue

Fixes #2811.

HexGrid with torus=True and an odd width or height leads to incorrect neighbor wrapping, where connections are not bidirectional. This configuration was previously allowed without validation, causing undefined behavior.

Implementation

-Added validation in HexGrid._validate_parameters to require even width and height when torus=True.

-A ValueError is raised for invalid configurations to prevent undefined topology.

Testing

-Added tests covering:

- Invalid toroidal grids with odd dimensions (error raised)

- Valid toroidal grids with even dimensions

- Non-toroidal grids with odd dimensions

- Ran the full test suite to ensure no regressions.

Additional Notes

This introduces validation for a previously unsupported configuration, causing affected models to fail fast with a clear error instead of producing inconsistent behavior.