Draft: Adds a quick cppcheck call into the build and fixes a bunch of issues detected by same

cppcheck is an optional build target, but it's been detecting some fun stuff

Among other changes:

• added initialisers in constructors
• marked some classes and methods final (I think needing to mark the method final is a questionable behaviour of cppcheck)
• marked some constructors/assignment operators as deleted
• ensured all headers that need it include config.h so there's no surprises if headers are included in a not-expected order.
• Removed some tests for null pointers where the pointer had been accessed prior to the null test