Stage 4cal (Calibrated Stellar Spectra)

[kevin218]

This PR adds a new step to the Eureka! pipeline. Stage 4cal produces calibrated stellar spectra over two regions (typically in and out of transit/eclipse) with uncertainties. In addition, I've added the following:

1. A new folder to Demos that steps through Stages 2, 3, and 4cal using NIRSpec G395H as an example
2. A suitable description of the new ECF parameters for the website
3. New tests that include a NIRSpec file from actual data, thus replacing the simulated FITS file.

[taylorbell57]

I haven't made it through all the files yet (and haven't looked at most of your new code yet), but here are some preliminary comments

[sebastian-zieba]

Hi, I'm currently testing this PR on some MIRI/LRS data and it works great!
Just wanted to say that I guess the run_eureka.py file should be updated too with something like
meta, spec, ds = s4cal.medianCalSpec(eventlabel, ecf_path=ecf_path)

[kevin218]

Hi, I'm currently testing this PR on some MIRI/LRS data and it works great! Just wanted to say that I guess the run_eureka.py file should be updated too with something like meta, spec, ds = s4cal.medianCalSpec(eventlabel, ecf_path=ecf_path)

I'm glad it's working out and thanks for the suggestion! I've added a suitable run_eureka.py file to the S4cal demos folder.