Zephyrus : Implement Rxuv computation (new formulas)

[EmmaPostolec]

After discussion/suggestions on the dev_zephyrus channel, here is a few propositions for Rxuv/Pxuv computation to implement for the escape :

• Kubishkina+2020 (Harrison) https://academic.oup.com/mnras/article/499/1/77/5905728
• Egger+2025 (Tim) https://arxiv.org/pdf/2502.07887
• Salz+2016 (Mara) https://www.aanda.org/articles/aa/pdf/2016/01/aa27042-15.pdf

Some of the formulation are valid fro hydrogen envelope (sub-Neptunes) but maybe we could use it for MO atmospheres ?

[nichollsh]

@EmmaPostolec the PR we merged does not close this, as it does not explore the other scalings for R_xuv based on the SW absorption.

[EmmaPostolec]

My mistake thanks @nichollsh !