Investigate continuum deficit

[jvshields]

I think our implementation of van noort 2011 was incorrect. I've updated the equation to accurately follow what is detailed in the paper. This seems to largely fix the continuum difference in the optical. In comparison to the solar luminosity in this wavelength regime, it improves the integrated flux from about 10% off to about 1% off.

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (5fd5a8f) 68.28% compared to head (5a262e7) 68.34%.

Files	Patch %	Lines
...is/radiation_field/radiation_field_solvers/base.py	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #168 +/- ## ========================================== + Coverage 68.28% 68.34% +0.05% ========================================== Files 31 31 Lines 1154 1153 -1 ========================================== Hits 788 788 + Misses 366 365 -1 ```

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[jvshields]

This branch was built on top of #167 so we should merge that one first.

[jvshields]

Is this testable? Can the equation this is all based on be part of the docstring?

The docstring points to the paper as well as the relevant equations, but it'd be a bit much for a docstring. This is the relevant bit of the paper

As for testability, this takes us between these two screenshots

so what I'm using as a test is just the low resolution flux of the solar spectrum (and korg).