Improved warnings with Medium2D

[caseyflex]

This adds a warning when a 2D geometry doesn't have a 2D medium.
@tylerflex it seems to break the adjoint tests, which has 0-thickness structures in a 2D sim. Is it possible to change these thicknesses to some other value, like td.inf? This may be more robust anyway without changing the intended behavior.

@tomflexcompute , this should also fix the plot_eps warning

[tylerflex]

@caseyflex I'm a bit confused. This seems to break both the regular and 2D adjoint tests with an error

E               pydantic.v1.error_wrappers.ValidationError: 1 validation error for JaxStructure
E               medium -> size -> 0
E                 ensure this value is greater than or equal to 0 (type=value_error.number.not_ge; limit_value=0)

Mediums shouldn't have sizes so that's strange.

Also, the adjoint tests don't have 2D geometries in them (I just verified on the regular test_adjoint_pipeline)

It seems this warning was also triggered in the tests as I see the warning message about 2D structure detected with no 2D medium.

Something seems strange here, I'm not sure what to make of it.

[tylerflex]

I can't help but wonder if this can just be simplified a lot

geom = values.get("geometry")
if geom is None:
    raise SetupError("'Structure.geometry' did not pass validation, can't check 2D medium".)

if isinstance(val, Medium2D) and not geom.is_2D:
    raise SetupError("Structure with a `Medium2D` medium needs a `2D` geometry.")

if geom.is_2D and not isinstance(val, Medium2D):
    zero_axis = geom.bounding_box.size.index(0)
    log.warning("found a geometry with < 3 dimensions not associated with a Medium2D ...")

with a simple property Geometry.is_2D that is implemented in each of the geometry subclasses?

[tylerflex]

Alternatives:

• add a Geometry.is_3D -> bool method and check if not geom.is_3D
• add a Geometry.ndims -> int and check if geom.ndims < 3

[caseyflex]

I think the complicated logic is a bit necessary, since we are checking different things. On the one hand, we need to check that if the medium is a Medium2D, the geometry must be a supported type and it must be 2D. Here, _normal_2dmaterial gives a detailed error message depending on the geometry and setup. On the other hand, if the bounding box has zero size in a certain direction and the medium is not Medium2D, it is helpful to give a warning. I'll add some comments to clarify this but I'm inclined to leave the logic as-is

[tylerflex]

Ok, the comments do help, looks good to me, thanks.