Add generic offworld model

[MayberryZoom]

Here's what the model currently looks like:

And in the dark:

Unfortunately, it seems pretty grainy in the light. I'm not sure what's wrong with it, so I'm putting up this PR as a draft until we can figure it out. My textures are somewhat scuffed, but shouldn't be causing that dramatic of an effect. My only thought is that maybe this is maybe I'm exporting the images wrong, but my GIMP settings were correct according to the Mercury Steam modding server.

Related issue: #240

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.98%. Comparing base (42ee71f) to head (68bb9b8).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #389   +/-   ##
=======================================
  Coverage   91.98%   91.98%           
=======================================
  Files          38       38           
  Lines        2159     2159           
=======================================
  Hits         1986     1986           
  Misses        173      173           

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