Epic: Breakup mono repo into multiple standalone repositories

[erri120]

Tasks:

• [x] Create a "meta"-repository
• [x] Create a template repository that uses the meta-repo
• [ ] Move libraries (and their tests) into their own repos (using the template):
  • [x] NexusMods.Paths (+ the testing helper lib)
  • [x] NexusMods.Hashing.xxHash64
  • [ ] NexusMods.FileExtractor
  • [ ] NexusMods.DataModel.RateLimiting
• [x] Convert project references into package references (#457)

The meta-repository will be included by every other repository as a submodule, and the included files will be symlinked. It should include files like .editorconfig, .gitignore, .gitattributes, LICENSE, and pre-setup .github/workflows.

The result of this should be standalone repositories that contain a single library, at best, working CI with test coverage and a release pipeline to push packages to NuGet. These repositories should all have the same layout, follow the same coding styles and the only differences should come from the code itself.

[Sewer56]

Potential candidate for closing in the future. I checked off the other projects that got moved away from main in order to be more 'up to date'.

Another potential candidate for this is 'Workspaces'. I also considered 'Diagnostics', however that's so intrinsically tied to our DataModel that it perhaps is better left as part of the App itself.

[erri120]

This can probably be closed.