Rework the Loadout Synchronizer

[halgari]

Implementation of the structure and tests of #626. This does not convert exsting games over to the new syncronizer, that will be done in a future pull request. All of the code is in the ALoadoutSyncronizer, start there or in ALoadoutSyncronizerTests to see usage.

[github-actions]

This PR conflicts with main. You need to rebase the PR before it can be merged.

[github-actions]

This PR doesn't conflict with main anymore. It can be merged after all status checks have passed and it has been reviewed.

[codecov]

Codecov Report

Merging #697 (4867557) into main (37c4ab0) will increase coverage by 64.39%.
Report is 14 commits behind head on main.
The diff coverage is 87.60%.

@@            Coverage Diff            @@
##           main     #697       +/-   ##
=========================================
+ Coverage      0   64.39%   +64.39%     
=========================================
  Files         0      656      +656     
  Lines         0    19205    +19205     
  Branches      0     1259     +1259     
=========================================
+ Hits          0    12368    +12368     
- Misses        0     6511     +6511     
- Partials      0      326      +326     

Flag	Coverage Δ
Linux	63.81% <87.60%> (?)
Windows	63.50% <87.60%> (?)
clean_environment_tests	64.38% <87.60%> (?)

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

Files	Coverage Δ
...xusMods.DataModel/Abstractions/EntityDictionary.cs	85.18% <100.00%> (ø)
...taModel/LoadoutSynchronizer/DefaultSynchronizer.cs	100.00% <100.00%> (ø)
...exusMods.DataModel/LoadoutSynchronizer/FileTree.cs	100.00% <100.00%> (ø)
....DataModel/LoadoutSynchronizer/FlattenedLoadout.cs	100.00% <100.00%> (ø)
...rc/NexusMods.DataModel/Loadouts/LoadoutRegistry.cs	75.00% <100.00%> (ø)
...NexusMods.DataModel/Loadouts/LoadoutSyncronizer.cs	95.88% <100.00%> (ø)
...usMods.DataModel/Loadouts/Markers/LoadoutMarker.cs	60.00% <100.00%> (ø)
src/NexusMods.DataModel/Loadouts/Mods/Mod.cs	100.00% <ø> (ø)
src/NexusMods.DataModel/Services.cs	96.77% <100.00%> (ø)
src/NexusMods.DataModel/Sorting/Rules/After.cs	100.00% <100.00%> (ø)
... and 17 more

... and 629 files with indirect coverage changes

[Al12rs]

Can I have a look before merging?

[Al12rs]

This is Unreachable, can be removed