Deprecate NEU code

[hannibal002]

Deprecate the entirety of neu classes and methods in SkyHanni.
This does not mean deprecating SkyHanni code that uses neu code, this means using something like #930 to add the deprecated annotation for IDEs when looking at neu code from inside SkyHanni project. This prevents us accidentally using neu code (and also encourages us to replace their internal logic in the long run)