Fix: use correct units for body_surface_temperature_in_K (K instead of K^4)

[kevinziroldi]

Problem

body_surface_temperature_in_K was documented and named as a temperature in Kelvin,
but the default value was 288**4, i.e. already T⁴. This leads to effectively using
T¹⁶ in the body IR term (_C_body_emission applies **4 again).

Fix

Change default from 288**4 to 288.0.

[gomezzz]

Hi @kevinziroldi ,

Thanks for catching this. You're right that 288**4 contradicts both the parameter name and the docstring, and _initialize_constants does square it up to T¹⁶.
Thankfully, I think, in practice it never took effect: ThermalModel isn't part of the public API, and its only construction site, ActorBuilder.set_thermal_model ( https://github.com/aidotse/PASEOS/blob/main/paseos/actors/actor_builder.py#L451 ) , always passes body_surface_temperature_in_K explicitly with a correct default of 288. So the bad value was only reachable by instantiating ThermalModel directly.
Still worth fixing. I'll take a closer look shortly! (Will likely aim to fix the CI first :) )