Made Before<,>.Other a required property

[Aragas]

the variant that After uses is what we want because it works better with our serializer

[codecov]

Codecov Report

Merging #764 (8882831) into main (bec16f5) will increase coverage by 0.74%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #764      +/-   ##
==========================================
+ Coverage   62.04%   62.78%   +0.74%     
==========================================
  Files         610      610              
  Lines       18455    18456       +1     
  Branches     1302     1302              
==========================================
+ Hits        11450    11588     +138     
+ Misses       6654     6523     -131     
+ Partials      351      345       -6     

Flag	Coverage Δ
Linux	62.09% <66.66%> (+0.05%)	⬆️
Windows	61.93% <66.66%> (?)
clean_environment_tests	62.77% <66.66%> (+0.72%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...exusMods.Games.BethesdaGameStudios/PluginSorter.cs	98.73% <100.00%> (ø)
src/NexusMods.DataModel/Sorting/Rules/Before.cs	50.00% <50.00%> (-50.00%)	⬇️

... and 31 files with indirect coverage changes