Fix conversions between axial and offset hex coords

[rparrett]

trafficstars

Fixes #414

This fixes conversions between AxialPos and (RowEvenPos, RowOddPos, ColEvenPos, ColOddPos) when coordinates are negative.

See https://www.redblobgames.com/grids/hexagons/#conversions

This seems correct, but it's currently unclear to me if similar work needs to be done in the shaders.

[rparrett]

I uncommented the stuff in the CI workflow that actually runs tests.

[rparrett]

I can't remember if some of these offsets should differ from redblob's numbers due to bevy's coordinate system or whatever.

We should double check that before merging.