added plot_units to simulation and scene classes

[dmarek-flex]

While working in the RF world I have been manually modifying plots so that the axes look good. But it is probably best to add that ability directly to tidy3d. I added an optional parameter to the Simulation and Scene classes that will automatically set the axes labels and title, along with a proper scaling of the tick labels.

Here is an example without setting plot_units:

And here when using "mm":

[tylerflex]

Thanks @dmarek-flex! This will definitely be nice to have

[dmarek-flex]

@tylerflex any idea why that set of tests failed?

[tylerflex]

Probably something doesn't like the μ.

[tylerflex]

potentially related to the regex? https://github.com/flexcompute/tidy3d/blob/develop/scripts/make_script.py#L69

[dmarek-flex]

@yaugenst-flex the more the merrier. I thought maybe you had changed make_script.py recently, but I think that was just the formatting commit.

[weiliangjin2021]

This is very helpful for now. Hopefully later we can set global units for time, length, etc.

[yaugenst-flex]

Looks great! Yeah make_script.py got formatted and I did some minor refactoring, didn't touch the actual functionality. There is currently a problem with generating scripts from simulations that contain DataArrays, but that's a bit tricky to sort out.