AstroObjectIllumination: Minor fixes

[leroyvn]

Description

This PR fixes minor issues with the new AstroObjectIllumination. Namely:

• Changed the default value of the angular_diameter parameter to something more useful in the context of remote sensing
• Fixed factory ID and filename inconsistencies
  *Apply a formatter pass
• Fix and simplify documentation

@wint3ria I removed a AstroObjectIllumination.astro_object() class method constructor because it didn't seem to be used anywhere; please let me know if this is useful somewhere and I'll happily roll back.

Checklist

• The code follows the relevant coding guidelines
• The code generates no new warnings
• The code is appropriately documented
• The code is tested to prove its function
• The feature branch is rebased on the current state of the main branch
• I updated the change log if relevant
• I give permission that the Eradiate project may redistribute my contributions under the terms of its license

[wint3ria]

The factory is indeed superfluous

[leroyvn]

Thanks @wint3ria, I'll merge this now.