Update to new `matvis` API

[r-pascua]

The matvis API as of version 1.3.0 is no longer compatible with the wrappers provided by hera_sim. Somehow this has eluded our tests, since version 1.2.1 is installed each time the tests are run (I'm guessing it's some weird logic with specifying matvis>=1.2.1 resulting in the lowest compatible version being chosen). One of the key breaking changes is that the conversions module was renamed to coordinates, but some of the contents had also been moved around. Another key change to address is the new shape of the returned visibility matrix. For now we maybe ought to pin v1.2.1 of matvis—what do you think, @steven-murray?

[steven-murray]

Thanks @r-pascua. This is addressed in #332, so we should prioritise getting that in, along with #339

[r-pascua]

Awesome, let me know if I can help move these along.