Add more unit tests to Radiation source model

[je-cook]

Description of issue / requirement to address

Add more tests to Radiation model its not particularly well covered at the moment

• Add more tests for radiation source model: radiation_profile #3328
• Add more tests for radiation source model: advective_transport #3329
• Add more tests for radiation source model: radiation_tools #3330
• Add more tests for radiation source model: flux_surfaces_maker #3331
• Add more tests for radiation source model: midplane_temperature_density #3332

[kj5248]

Created new issues to split up this issue more for files in radiation_transport folder (not including neutronics): #3328 #3329 #3330 #3331 #3332