Full migration to c++26 modules via a separate branch

I think mixing headers and header/sources and modules in the same repo with multiple build systems is a very bad idea. I propose that a new branch be created for a fixed set c++26 migration. - Only cmake - Only C++26 - Filesystem always exists, rtti is always there. etc etc, enough to get rid of the macro header. - Only named modules, so we can get rid of weird inline and nodiscard macros. - Only catch 3 as the testing framework. How would this be done? Each impl header pair becomes a module partition. Interface module exports these. Testing is done for the module.