This is cleanup based on both new .NET functionality (in 6 and 7) as well as a ton of simplifications and things that were missed that were caught due to the cleanup.
This was the last of the major bits of code that was technically distinct from Cleaning. This means that each of the bits of functionality that used to all be in Cleaner are split out into their approrpriate classes.
This had the potential to cause a lot of issues the way it was. Moving the actual functionality for cleaning, filtering, and applying extras to their appropriate classes allows for less redirection when calling into the code. Modification as a class was essentially a shell around things that should have just been a single call.
This change ended up being three-fold:
1. Remove the entirely unused header field filters
2. Move filter running to their appropriate filter classes
3. Separate out DatItem filters into more managable private methods
