Structures in absorber trigers a warning about PML

[tomflexcompute]

When there is a structure completely inside the absorber boundary, it triggers a warning

WARNING: A bound of Simulation.structures[94] was
detected as being within the simulation PML. We
recommend extending structures to infinity or
completely outside of the simulation PML to avoid
unexpected effects when the structures are not
translationally invariant within the PML.

This seems to be related to the pml_thicknesses here actually includes not just PML but absorber as well. Therefore _validate_no_structures_pml returns a warning for structures in absorber too.

[momchil-flex]

I am wondering if we should change the message instead of completely removing the warning for Absorbers. Yes, absorbers may not diverge, but I feel like this could still be indicative of an unintended setup in some cases, e.g. this can create extra reflections if the users just didn't realize that they didn't extend their structures through. What do you think?

[tomflexcompute]

Yeah that sounds good. As long as we can eliminate the confusion from the warning it should be fine.