`JaxSimulation.epsilon` ignores `input_structures`

[tylerflex]

Another annoying case (like plot) where we need to convert to_simulation() first.

[tylerflex]

Note for later: maybe when validating input_structures, we can just convert to regular Structure, add to structures, and then do everything else normally. Similar to how the permittivity_jax field works after the refactor.

[tylerflex]

Somewhat related: seems JaxSimulationData.plot_field also doesn't work when applied to an output field monitor because JaxSimulation.get_monitor_by_name doesn't look in output_monitors.

I think I'll just try to do a refactor where the JaxSimulation input_structures and output_monitors are converted and appended to their structures and input_structures fields at init time and that should solve this and whatever other issues exist.

[tylerflex]

fixed by #1601