Closes#3921
Not sure if the RTC handling is correct (always 0x20 length?) but at least we have a non-fixed-sized header handled with some leniency for different builds.
With the new version of Visual Studio bringing C# 12, we can revise our logic for better readability as well as use new methods/APIs introduced in the .NET 8.0 BCL.
GCI, DSV, DUC are already supported, so I've written the abstraction for those and seed the Handler list on startup.
Can add a new class with recognition via SaveUtil.Handlers.Add(myHandler);